kernel/compat.c: mark expected switch fall-throughs

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

This patch aims to suppress 3 missing-break-in-switch false positives
on some architectures.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: Deepa Dinamani <deepa.kernel@gmail.com>
Cc: Gustavo A. R. Silva <gustavo@embeddedor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/compat.c

@@ -346,8 +346,11 @@ get_compat_sigset(sigset_t *set, const compat_sigset_t __user *compat)
 		return -EFAULT;
 	switch (_NSIG_WORDS) {
 	case 4: set->sig[3] = v.sig[6] | (((long)v.sig[7]) << 32 );
+		/* fall through */
 	case 3: set->sig[2] = v.sig[4] | (((long)v.sig[5]) << 32 );
+		/* fall through */
 	case 2: set->sig[1] = v.sig[2] | (((long)v.sig[3]) << 32 );
+		/* fall through */
 	case 1: set->sig[0] = v.sig[0] | (((long)v.sig[1]) << 32 );
 	}
 #else