staging: rtl8712: fix race condition

commit 1422b526

 upstream.

In probe function, request_firmware_nowait() is called to load firmware
asynchronously. At completion of firmware loading, register_netdev() is
called. However, a mutex needed by netdev is initialized after the call
to request_firmware_nowait(). Consequently, it can happen that
register_netdev() is called before the driver is ready.

Move the mutex initialization into r8712_init_drv_sw(), which is called
before request_firmware_nowait().

Reported-by:  <syzbot+b08315e8cf5a78eed03c@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/linux-staging/000000000000d9d4560601b8e0d7@google.com/T/#u
Fixes: 8c213fa5

 ("staging: r8712u: Use asynchronous firmware loading")
Cc: stable <stable@kernel.org>
Signed-off-by: Nam Cao <namcaov@gmail.com>
Link: https://lore.kernel.org/r/20230731110620.116562-1-namcaov@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>