cfg80211: 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/115Signed-off-by: NGustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/ed94a115106fa9c6df94d09b2a6c5791c618c4f2.1605896059.git.gustavoars@kernel.orgSigned-off-by: NJohannes Berg <johannes.berg@intel.com>

net/wireless/util.c

@@ -335,6 +335,7 @@ int cfg80211_validate_key_settings(struct cfg80211_registered_device *rdev,
 	case WLAN_CIPHER_SUITE_WEP104:
 		if (key_idx > 3)
 			return -EINVAL;
+		break;
 	default:
 		break;
 	}