staging: rtl8712: fix uninit-value in usb_read8() and friends

In the Linux kernel, the following vulnerability has been resolved:

staging: rtl8712: fix uninit-value in usb_read8() and friends

When r8712_usbctrl_vendorreq() returns negative, 'data' in
usb_read{8,16,32} will not be initialized.

BUG: KMSAN: uninit-value in string_nocheck lib/vsprintf.c:643 [inline]
BUG: KMSAN: uninit-value in string+0x4ec/0x6f0 lib/vsprintf.c:725
string_nocheck lib/vsprintf.c:643 [inline]
string+0x4ec/0x6f0 lib/vsprintf.c:725
vsnprintf+0x2222/0x3650 lib/vsprintf.c:2806
va_format lib/vsprintf.c:1704 [inline]
pointer+0x18e6/0x1f70 lib/vsprintf.c:2443
vsnprintf+0x1a9b/0x3650 lib/vsprintf.c:2810
vprintk_store+0x537/0x2150 kernel/printk/printk.c:2158
vprintk_emit+0x28b/0xab0 kernel/printk/printk.c:2256
dev_vprintk_emit+0x5ef/0x6d0 drivers/base/core.c:4604
dev_printk_emit+0x1dd/0x21f drivers/base/core.c:4615
__dev_printk+0x3be/0x440 drivers/base/core.c:4627
_dev_info+0x1ea/0x22f drivers/base/core.c:4673
r871xu_drv_init+0x1929/0x3070 drivers/staging/rtl8712/usb_intf.c:401
usb_probe_interface+0xf19/0x1600 drivers/usb/core/driver.c:396
really_probe+0x6c7/0x1350 drivers/base/dd.c:621
__driver_probe_device+0x3e9/0x530 drivers/base/dd.c:752
driver_probe_device drivers/base/dd.c:782 [inline]
__device_attach_driver+0x79f/0x1120 drivers/base/dd.c:899
bus_for_each_drv+0x2d6/0x3f0 drivers/base/bus.c:427
__device_attach+0x593/0x8e0 drivers/base/dd.c:970
device_initial_probe+0x4a/0x60 drivers/base/dd.c:1017
bus_probe_device+0x17b/0x3e0 drivers/base/bus.c:487
device_add+0x1fff/0x26e0 drivers/base/core.c:3405
usb_set_configuration+0x37e9/0x3ed0 drivers/usb/core/message.c:2170
usb_generic_driver_probe+0x13c/0x300 drivers/usb/core/generic.c:238
usb_probe_device+0x309/0x570 drivers/usb/core/driver.c:293
really_probe+0x6c7/0x1350 drivers/base/dd.c:621
__driver_probe_device+0x3e9/0x530 drivers/base/dd.c:752
driver_probe_device drivers/base/dd.c:782 [inline]
__device_attach_driver+0x79f/0x1120 drivers/base/dd.c:899
bus_for_each_drv+0x2d6/0x3f0 drivers/base/bus.c:427
__device_attach+0x593/0x8e0 drivers/base/dd.c:970
device_initial_probe+0x4a/0x60 drivers/base/dd.c:1017
bus_probe_device+0x17b/0x3e0 drivers/base/bus.c:487
device_add+0x1fff/0x26e0 drivers/base/core.c:3405
usb_new_device+0x1b91/0x2950 drivers/usb/core/hub.c:2566
hub_port_connect drivers/usb/core/hub.c:5363 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5507 [inline]
port_event drivers/usb/core/hub.c:5665 [inline]
hub_event+0x58e3/0x89e0 drivers/usb/core/hub.c:5747
process_one_work+0xdb6/0x1820 kernel/workqueue.c:2289
worker_thread+0x10d0/0x2240 kernel/workqueue.c:2436
kthread+0x3c7/0x500 kernel/kthread.c:376
ret_from_fork+0x1f/0x30

Local variable data created at:
usb_read8+0x5d/0x130 drivers/staging/rtl8712/usb_ops.c:33
r8712_read8+0xa5/0xd0 drivers/staging/rtl8712/rtl8712_io.c:29

KMSAN: uninit-value in r871xu_drv_init
https://syzkaller.appspot.com/bug?id=3cd92b1d85428b128503bfa7a250294c9ae00bd8