Staging: rtl8723au: Remove return in void function

WARNING: void function return statements are not generally useful
Remove return in void function. That was found by running checkpatch.

Signed-off-by: Melike Yurtoglu <aysemelikeyurtoglu@gmail.com>
Reviewed-by: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>