staging/lustre: fix return value check in libcfs_sock_ioctl()

In case of error, the function sock_alloc_file() returns ERR_PTR()
and never returns NULL. The NULL test in the return value check
should be replaced with IS_ERR().
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/libcfs/linux/linux-tcpip.c

@@ -59,9 +59,9 @@ libcfs_sock_ioctl(int cmd, unsigned long arg)
 	}
 
 	sock_filp = sock_alloc_file(sock, 0, NULL);
-	if (!sock_filp) {
+	if (IS_ERR(sock_filp)) {
 		sock_release(sock);
-		rc = -ENOMEM;
+		rc = PTR_ERR(sock_filp);
 		goto out;
 	}