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>

lib/vsprintf.c

@@ -1265,7 +1265,7 @@ char *mac_address_string(char *buf, char *end, u8 *addr,
 
 	case 'R':
 		reversed = true;
-		/* fall through */
+		fallthrough;
 
 	default:
 		separator = ':';
@@ -1681,7 +1681,8 @@ char *uuid_string(char *buf, char *end, const u8 *addr,
 
 	switch (*(++fmt)) {
 	case 'L':
-		uc = true;		/* fall-through */
+		uc = true;
+		fallthrough;
 	case 'l':
 		index = guid_index;
 		break;
@@ -2218,7 +2219,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 	case 'S':
 	case 's':
 		ptr = dereference_symbol_descriptor(ptr);
-		/* Fallthrough */
+		fallthrough;
 	case 'B':
 		return symbol_string(buf, end, ptr, spec, fmt);
 	case 'R':
@@ -2449,7 +2450,7 @@ qualifier:
 
 	case 'x':
 		spec->flags |= SMALL;
-		/* fall through */
+		fallthrough;
 
 	case 'X':
 		spec->base = 16;
@@ -2467,7 +2468,7 @@ qualifier:
 		 * utility, treat it as any other invalid or
 		 * unsupported format specifier.
 		 */
-		/* Fall-through */
+		fallthrough;
 
 	default:
 		WARN_ONCE(1, "Please remove unsupported %%%c in format string\n", *fmt);
@@ -3410,10 +3411,10 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
 			break;
 		case 'i':
 			base = 0;
-			/* fall through */
+			fallthrough;
 		case 'd':
 			is_sign = true;
-			/* fall through */
+			fallthrough;
 		case 'u':
 			break;
 		case '%':