serial: 8250_bcm7271: Fix error handling in brcmuart_init()

serial: 8250_bcm7271: Fix error handling in brcmuart_init()

A problem about 8250_bcm7271 create debugfs failed is triggered with the
following log given:

 [  324.516635] debugfs: Directory 'bcm7271-uart' with parent '/' already present!

The reason is that brcmuart_init() returns platform_driver_register()
directly without checking its return value, if platform_driver_register()
failed, it returns without destroy the newly created debugfs, resulting
the debugfs of 8250_bcm7271 can never be created later.

 brcmuart_init()
   debugfs_create_dir() # create debugfs directory
   platform_driver_register()
     driver_register()
       bus_add_driver()
         priv = kzalloc(...) # OOM happened
   # return without destroy debugfs directory

Fix by removing debugfs when platform_driver_register() returns error.

Fixes: 41a469482de2 ("serial: 8250: Add new 8250-core based Broadcom STB driver")
Signed-off-by: Yuan Can <yuancan@huawei.com>
Link: https://lore.kernel.org/r/20221109072110.117291-2-yuancan@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>