IB/core: Fix input len in multiple user verbs

Most user verbs pass user data to the kernel with the inclusion of the
ib_uverbs_cmd_hdr structure. This is problematic because the vendor has
no ideas if the verb was called by a legacy verb or an extended verb.
Also, the incosistency between the verbs is confusing.

Fixes: 565197dd8f ("IB/core: Extend ib_uverbs_create_cq")
Signed-off-by: Ram Amrani <Ram.Amrani@cavium.com>
Signed-off-by: Ariel Elior <Ariel.Elior@cavium.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/mlx5/cq.c

@@ -751,10 +751,8 @@ static int create_cq_user(struct mlx5_ib_dev *dev, struct ib_udata *udata,
 	void *cqc;
 	int err;
 
-	ucmdlen =
-		(udata->inlen - sizeof(struct ib_uverbs_cmd_hdr) <
-		 sizeof(ucmd)) ? (sizeof(ucmd) -
-				  sizeof(ucmd.reserved)) : sizeof(ucmd);
+	ucmdlen = udata->inlen < sizeof(ucmd) ?
+		  (sizeof(ucmd) - sizeof(ucmd.reserved)) : sizeof(ucmd);
 
 	if (ib_copy_from_udata(&ucmd, udata, ucmdlen))
 		return -EFAULT;