staging: r8712u: Use asynchronous firmware loading

In https://bugs.archlinux.org/task/27996

, failure of driver r8712u is
reported, with a timeout during module loading due to synchronous loading
of the firmware. The code now uses request_firmware_nowait().

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>