pinctrl: lpc18xx: mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Addresses-Coverity-ID: 1292308 ("Missing break in switch")
Addresses-Coverity-ID: 1292309 ("Missing break in switch")
Addresses-Coverity-ID: 1309546 ("Missing break in switch")
Addresses-Coverity-ID: 1357369 ("Missing break in switch")
Addresses-Coverity-ID: 1357389 ("Missing break in switch")
Reviewed-by: Vladimir Zapolskiy <[e-mail]>
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

drivers/pinctrl/pinctrl-lpc18xx.c

···
 		*arg = (reg & LPC18XX_SCU_PIN_EHD_MASK) >> LPC18XX_SCU_PIN_EHD_POS;
 		switch (*arg) {
 		case 3: *arg += 5;
+			/* fall through */
 		case 2: *arg += 5;
+			/* fall through */
 		case 1: *arg += 3;
+			/* fall through */
 		case 0: *arg += 4;
 		}
 		break;
···
 
 		switch (param_val) {
 		case 20: param_val -= 5;
+			 /* fall through */
 		case 14: param_val -= 5;
+			 /* fall through */
 		case  8: param_val -= 3;
+			 /* fall through */
 		case  4: param_val -= 4;
 			 break;
 		default: