net: dsa: realtek: use gpiod_set_value_cansleep for reset GPIO

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

net: dsa: realtek: use gpiod_set_value_cansleep for reset GPIO

rtl83xx_reset_assert() and rtl83xx_reset_deassert() are only called from
the probe path, which may sleep and is not timing-critical. When the
reset GPIO is provided by a sleeping controller such as an I2C I/O
expander, gpiod_set_value() warns:

WARNING: drivers/gpio/gpiolib.c:4030 at gpiod_set_value+0x44/0x80, CPU#1: kworker/u16:4/61
Hardware name: B&O MAP CA33 Rev f (UNKNOWN) (DT)
Workqueue: events_unbound deferred_probe_work_func
pc : gpiod_set_value+0x44/0x80
lr : rtl83xx_probe+0x1d8/0x3a0
Call trace:
gpiod_set_value+0x44/0x80 (P)
rtl83xx_probe+0x1d8/0x3a0
realtek_mdio_probe+0x24/0xa0
mdio_probe+0x38/0x78
really_probe+0xc4/0x3e0
__driver_probe_device+0x15c/0x1b8
driver_probe_device+0xb4/0x120
__device_attach_driver+0xb8/0x1a0
bus_for_each_drv+0x88/0xf0
__device_attach+0xa0/0x1d8
device_initial_probe+0x54/0x68
bus_probe_device+0x38/0xa0
deferred_probe_work_func+0xb8/0x120
process_one_work+0x184/0x4e8
worker_thread+0x188/0x308
kthread+0x130/0x150
ret_from_fork+0x10/0x20

Switch both helpers to gpiod_set_value_cansleep() so such a reset GPIO can
be used without triggering the warning.

The reset GPIO has been driven with the non-sleeping gpiod_set_value()
since the driver was added in v4.19. The call has since been refactored
across several files - from realtek-smi.c / realtek-mdio.c into the common
rtl83xx.c module and then into the rtl83xx_reset_assert() and
rtl83xx_reset_deassert() helpers (both in v6.9). This patch therefore
applies as-is only to kernels that carry those helpers (v6.9+); older
stable kernels need the same gpiod_set_value_cansleep() conversion at the
corresponding open-coded call sites.