auxdisplay: panel: Change comments to silence fallthrough warnings

Compiling with W=1 with gcc 7.2.0 gives 3 warnings like:

  drivers/auxdisplay/panel.c: In function ‘panel_process_inputs’:
  drivers/auxdisplay/panel.c:1374:17: warning: this statement may fall
  through [-Wimplicit-fallthrough=]

Cc: Willy Tarreau <w@1wt.eu>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>

drivers/auxdisplay/panel.c

@@ -1372,7 +1372,7 @@ static void panel_process_inputs(void)
 				break;
 			input->rise_timer = 0;
 			input->state = INPUT_ST_RISING;
-			/* no break here, fall through */
+			/* fall through */
 		case INPUT_ST_RISING:
 			if ((phys_curr & input->mask) != input->value) {
 				input->state = INPUT_ST_LOW;
@@ -1385,11 +1385,11 @@ static void panel_process_inputs(void)
 			}
 			input->high_timer = 0;
 			input->state = INPUT_ST_HIGH;
-			/* no break here, fall through */
+			/* fall through */
 		case INPUT_ST_HIGH:
 			if (input_state_high(input))
 				break;
-			/* no break here, fall through */
+			/* fall through */
 		case INPUT_ST_FALLING:
 			input_state_falling(input);
 		}