cifs: fix memory leak of pneg_inbuf on -EOPNOTSUPP ioctl case

Currently in the case where SMB2_ioctl returns the -EOPNOTSUPP error
there is a memory leak of pneg_inbuf. Fix this by returning via
the out_free_inbuf exit path that will perform the relevant kfree.

Addresses-Coverity: ("Resource leak")
Fixes: 969ae8e8 ("cifs: Accept validate negotiate if server return NT_STATUS_NOT_SUPPORTED")
CC: Stable <stable@vger.kernel.org> # v5.1+
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2pdu.c

@@ -1054,7 +1054,8 @@ int smb3_validate_negotiate(const unsigned int xid, struct cifs_tcon *tcon)
 		 * not supported error. Client should accept it.
 		 */
 		cifs_dbg(VFS, "Server does not support validate negotiate\n");
-		return 0;
+		rc = 0;
+		goto out_free_inbuf;
 	} else if (rc != 0) {
 		cifs_dbg(VFS, "validate protocol negotiate failed: %d\n", rc);
 		rc = -EIO;