drm/mediatek: dsi: Store driver data before invoking mipi_dsi_host_register

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

drm/mediatek: dsi: Store driver data before invoking mipi_dsi_host_register

The call to mipi_dsi_host_register triggers a callback to mtk_dsi_bind,
which uses dev_get_drvdata to retrieve the mtk_dsi struct, so this
structure needs to be stored inside the driver data before invoking it.

As drvdata is currently uninitialized it leads to a crash when
registering the DSI DRM encoder right after acquiring
the mode_config.idr_mutex, blocking all subsequent DRM operations.

Fixes the following crash during mediatek-drm probe (tested on Xiaomi
Smart Clock x04g):

Unable to handle kernel NULL pointer dereference at virtual address
0000000000000040
[...]
Modules linked in: mediatek_drm(+) drm_display_helper cec drm_client_lib
drm_dma_helper drm_kms_helper panel_simple
[...]
Call trace:
drm_mode_object_add+0x58/0x98 (P)
__drm_encoder_init+0x48/0x140
drm_encoder_init+0x6c/0xa0
drm_simple_encoder_init+0x20/0x34 [drm_kms_helper]
mtk_dsi_bind+0x34/0x13c [mediatek_drm]
component_bind_all+0x120/0x280
mtk_drm_bind+0x284/0x67c [mediatek_drm]
try_to_bring_up_aggregate_device+0x23c/0x320
__component_add+0xa4/0x198
component_add+0x14/0x20
mtk_dsi_host_attach+0x78/0x100 [mediatek_drm]
mipi_dsi_attach+0x2c/0x50
panel_simple_dsi_probe+0x4c/0x9c [panel_simple]
mipi_dsi_drv_probe+0x1c/0x28
really_probe+0xc0/0x3dc
__driver_probe_device+0x80/0x160
driver_probe_device+0x40/0x120
__device_attach_driver+0xbc/0x17c
bus_for_each_drv+0x88/0xf0
__device_attach+0x9c/0x1cc
device_initial_probe+0x54/0x60
bus_probe_device+0x34/0xa0
device_add+0x5b0/0x800
mipi_dsi_device_register_full+0xdc/0x16c
mipi_dsi_host_register+0xc4/0x17c
mtk_dsi_probe+0x10c/0x260 [mediatek_drm]
platform_probe+0x5c/0xa4
really_probe+0xc0/0x3dc
__driver_probe_device+0x80/0x160
driver_probe_device+0x40/0x120
__driver_attach+0xc8/0x1f8
bus_for_each_dev+0x7c/0xe0
driver_attach+0x24/0x30
bus_add_driver+0x11c/0x240
driver_register+0x68/0x130
__platform_register_drivers+0x64/0x160
mtk_drm_init+0x24/0x1000 [mediatek_drm]
do_one_initcall+0x60/0x1d0
do_init_module+0x54/0x240
load_module+0x1838/0x1dc0
init_module_from_file+0xd8/0xf0
__arm64_sys_finit_module+0x1b4/0x428
invoke_syscall.constprop.0+0x48/0xc8
do_el0_svc+0x3c/0xb8
el0_svc+0x34/0xe8
el0t_64_sync_handler+0xa0/0xe4
el0t_64_sync+0x198/0x19c
Code: 52800022 941004ab 2a0003f3 37f80040 (29005a80)