docs: Use fallthrough pseudo-keyword

Replace /* fall through */ comment with fallthrough, make
it align with original process/coding-style.rst

Signed-off-by: Wei Ming Chen <jj251510319013@gmail.com>
Link: https://lore.kernel.org/r/20210515155142.2490-1-jj251510319013@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/translations/it_IT/process/coding-style.rst

@@ -62,7 +62,7 @@ i ``case``.  Un esempio.:
 	case 'K':
 	case 'k':
 		mem <<= 10;
-		/* fall through */
+		fallthrough;
 	default:
 		break;
 	}

Documentation/translations/zh_CN/process/coding-style.rst

@@ -61,7 +61,7 @@ Linux 内核代码风格
 	case 'K':
 	case 'k':
 		mem <<= 10;
-		/* fall through */
+		fallthrough;
 	default:
 		break;
 	}