staging: alarm-dev: Set the license to GPL

Adding "GPL" license to fix a warning while compiling as
module.

CC: Brian Swetland <swetland@google.com>
Signed-off-by: Pramod Gurav <pramod.gurav.etc@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>