cifsd: fix a IS_ERR() vs NULL bug

mainline inclusion
from mainline-5.15-rc1
commit 8ef32967
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I60T7G
CVE: NA

Reference: https://git.kernel.org/torvalds/linux/c/8ef329670657

-------------------------------

The smb_direct_alloc_sendmsg() function never returns NULL, it only
returns error pointers so the check needs to be updated.
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: NNamjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: NSteve French <stfrench@microsoft.com>
Signed-off-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NZhong Jinghua <zhongjinghua@huawei.com>

fs/cifsd/transport_rdma.c

@@ -997,8 +997,8 @@ static int smb_direct_create_header(struct smb_direct_transport *t,
 	int ret;
 
 	sendmsg = smb_direct_alloc_sendmsg(t);
-	if (!sendmsg)
-		return -ENOMEM;
+	if (IS_ERR(sendmsg))
+		return PTR_ERR(sendmsg);
 
 	/* Fill in the packet header */
 	packet = (struct smb_direct_data_transfer *)sendmsg->packet;