staging: rtl8723au: Fixes unnecessary return warning

This patch fixes checkpatch.pl warning in rtw_mlme_ext.c file.
WARNING: void function return statements are not generally useful

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
Reviewed-by: Julian Calaby <julian.calaby@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>