treewide: Use fallthrough pseudo-keyword

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1]. Also, remove unnecessary
fall-through markings when it is the case.

[1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

drivers/rtc/rtc-m41t80.c

@@ -740,7 +740,7 @@ static int wdt_ioctl(struct file *file, unsigned int cmd,
 			return -EINVAL;
 		wdt_margin = new_margin;
 		wdt_ping();
-		/* Fall through */
+		fallthrough;
 	case WDIOC_GETTIMEOUT:
 		return put_user(wdt_margin, (int __user *)arg);
 

drivers/rtc/rtc-pcf85063.c

@@ -353,7 +353,7 @@ static int pcf85063_load_capacitance(struct pcf85063 *pcf85063,
 	default:
 		dev_warn(&pcf85063->rtc->dev, "Unknown quartz-load-femtofarads value: %d. Assuming 7000",
 			 load);
-		/* fall through */
+		fallthrough;
 	case 7000:
 		break;
 	case 12500:

drivers/rtc/rtc-pcf8523.c

@@ -108,7 +108,7 @@ static int pcf8523_load_capacitance(struct i2c_client *client)
 	default:
 		dev_warn(&client->dev, "Unknown quartz-load-femtofarads value: %d. Assuming 12500",
 			 load);
-		/* fall through */
+		fallthrough;
 	case 12500:
 		value |= REG_CONTROL1_CAP_SEL;
 		break;

drivers/rtc/rtc-stmp3xxx.c

@@ -331,7 +331,7 @@ static int stmp3xxx_rtc_probe(struct platform_device *pdev)
 	default:
 		dev_warn(&pdev->dev,
 			 "invalid crystal-freq specified in device-tree. Assuming no crystal\n");
-		/* fall-through */
+		fallthrough;
 	case 0:
 		/* keep XTAL on in low-power mode */
 		pers0_set = STMP3XXX_RTC_PERSISTENT0_XTAL24MHZ_PWRUP;