Input: matrix-keymap - provide proper module license

commit 55220bb3 upstream.

The matrix-keymap module is currently lacking a proper module license,
add one so we don't have this module tainting the entire kernel.  This
issue has been present since commit 1932811f ("Input: matrix-keymap
- uninline and prepare for device tree support")

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>