staging: vt6656: 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: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/5a5a8f2489fbf61f65f0241c349737f7c9ad59ca.1605896060.git.gustavoars@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vt6656/main_usb.c

@@ -914,6 +914,7 @@ static int vnt_set_key(struct ieee80211_hw *hw, enum set_key_cmd cmd,
 
 			vnt_mac_disable_keyentry(priv, key->hw_key_idx);
 		}
+		break;
 
 	default:
 		break;