cifsd: Fix an error code in smb2_read()

This code is assigning the wrong variable to "err" so it returns
zero/success instead of -ENOMEM.

Fixes: 788b6f45c1d2 ("cifsd: add server-side procedures for SMB3")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifsd/smb2pdu.c

@@ -6200,7 +6200,7 @@ int smb2_read(struct ksmbd_work *work)
 		work->aux_payload_buf = ksmbd_alloc_response(length);
 	}
 	if (!work->aux_payload_buf) {
-		err = nbytes;
+		err = -ENOMEM;
 		goto out;
 	}