staging: media: lirc: fixed sparse warnings by adding __user annotations in lirc_serial.c

This patch fixes sparse warning by adding __user annotations in
lirc_serial.c

Signed-off-by: Archana kumari <archanakumari959@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>