security: keys: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix a warning
by explicitly adding a break statement instead of letting the code fall
through to the next case.

Link: https://github.com/KSPP/linux/issues/115
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Reviewed-by: Ben Boeckel <mathstuf@gmail.com>

security/keys/process_keys.c

@@ -783,6 +783,7 @@ try_again:
 				if (need_perm != KEY_AUTHTOKEN_OVERRIDE &&
 				    need_perm != KEY_DEFER_PERM_CHECK)
 					goto invalid_key;
+				break;
 			case 0:
 				break;
 			}