Input: mt6779-keypad - add missing linux/input.h include

We are going to clean up matrix_keymap.h from unnecessary includes,
so the driver needs to include API that it uses directly.
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220923194738.927408-3-dmitry.torokhov@gmail.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/keyboard/mt6779-keypad.c

@@ -5,6 +5,7 @@
  */
 #include <linux/bitops.h>
 #include <linux/clk.h>
+#include <linux/input.h>
 #include <linux/input/matrix_keypad.h>
 #include <linux/interrupt.h>
 #include <linux/module.h>