drm/ingenic: Fix missing platform_driver_unregister() call in ingenic_drm_init()

drm/ingenic: Fix missing platform_driver_unregister() call in ingenic_drm_init()

A problem about modprobe ingenic-drm failed is triggered with the following
log given:

 [  303.561088] Error: Driver 'ingenic-ipu' is already registered, aborting...
 modprobe: ERROR: could not insert 'ingenic_drm': Device or resource busy

The reason is that ingenic_drm_init() returns platform_driver_register()
directly without checking its return value, if platform_driver_register()
failed, it returns without unregistering ingenic_ipu_driver_ptr, resulting
the ingenic-drm can never be installed later.
A simple call graph is shown as below:

 ingenic_drm_init()
   platform_driver_register() # ingenic_ipu_driver_ptr are registered
   platform_driver_register()
     driver_register()
       bus_add_driver()
         priv = kzalloc(...) # OOM happened
   # return without unregister ingenic_ipu_driver_ptr

Fixing this problem by checking the return value of
platform_driver_register() and do platform_unregister_drivers() if
error happened.

Fixes: fc1acf317b01 ("drm/ingenic: Add support for the IPU")
Signed-off-by: Yuan Can <yuancan@huawei.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20221104064512.8569-1-yuancan@huawei.com