staging: r8712u: Fix possible out-of-bounds index with TKIP and AES keys

Array XGrpKey has only 2 elements and uses (keyid - 1) as the index, which
allows the possibility of memory corruption from an out-of-bounds index.

This problem was reported by a new version of smatch.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NLarry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/staging/rtl8712/rtl871x_mlme.c

@@ -1281,12 +1281,16 @@ sint r8712_set_key(struct _adapter *adapter,
 			psecuritypriv->DefKey[keyid].skey, keylen);
 		break;
 	case _TKIP_:
+		if (keyid < 1 || keyid > 2)
+			return _FAIL;
 		keylen = 16;
 		memcpy(psetkeyparm->key,
 			&psecuritypriv->XGrpKey[keyid - 1], keylen);
 		psetkeyparm->grpkey = 1;
 		break;
 	case _AES_:
+		if (keyid < 1 || keyid > 2)
+			return _FAIL;
 		keylen = 16;
 		memcpy(psetkeyparm->key,
 			&psecuritypriv->XGrpKey[keyid - 1], keylen);