Staging: rtl8712: Cleanup coding style warning

This patch fixes checkpatch warning about multiple line dereference.

Signed-off-by: Khoa Tran Minh <ktm8@posteo.de>
Link: https://lore.kernel.org/r/YLZ1fc7BsaTo+ixQ@rue.localhost


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>