Input: matrix-keymap - provide a proper module license

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>
CC: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/matrix-keymap.c

@@ -23,6 +23,7 @@
 #include <linux/input.h>
 #include <linux/of.h>
 #include <linux/export.h>
+#include <linux/module.h>
 #include <linux/input/matrix_keypad.h>
 
 static bool matrix_keypad_map_key(struct input_dev *input_dev,
@@ -161,3 +162,5 @@ int matrix_keypad_build_keymap(const struct matrix_keymap_data *keymap_data,
 	return 0;
 }
 EXPORT_SYMBOL(matrix_keypad_build_keymap);
+
+MODULE_LICENSE("GPL");