pinctrl: lpc18xx: Use fallthrough pseudo-keyword

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1].

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-throughSigned-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20200716212109.GA17525@embeddedorSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/pinctrl-lpc18xx.c

@@ -838,11 +838,11 @@ static int lpc18xx_pconf_get_pin(struct pinctrl_dev *pctldev, unsigned param,
 		*arg = (reg & LPC18XX_SCU_PIN_EHD_MASK) >> LPC18XX_SCU_PIN_EHD_POS;
 		switch (*arg) {
 		case 3: *arg += 5;
-			/* fall through */
+			fallthrough;
 		case 2: *arg += 5;
-			/* fall through */
+			fallthrough;
 		case 1: *arg += 3;
-			/* fall through */
+			fallthrough;
 		case 0: *arg += 4;
 		}
 		break;
@@ -1057,11 +1057,11 @@ static int lpc18xx_pconf_set_pin(struct pinctrl_dev *pctldev, unsigned param,
 
 		switch (param_val) {
 		case 20: param_val -= 5;
-			 /* fall through */
+			fallthrough;
 		case 14: param_val -= 5;
-			 /* fall through */
+			fallthrough;
 		case  8: param_val -= 3;
-			 /* fall through */
+			fallthrough;
 		case  4: param_val -= 4;
 			 break;
 		default: