vdpa/mlx5: Fix uninitialised variable in core/mr.c

If the kernel is unable to allocate memory for the variable dmr then
err will be returned without being set. Set err to -ENOMEM in this
case.

Fixes: 94abbccd ("vdpa/mlx5: Add shared memory registration code")
Addresses-Coverity: ("Uninitialized variables")
Signed-off-by: Alex Dewar <alex.dewar@gmx.co.uk>
Link: https://lore.kernel.org/r/20200806185625.67344-1-alex.dewar@gmx.co.ukSigned-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Eli Cohen <eli@mellanox.com>

drivers/vdpa/mlx5/core/mr.c

@@ -319,8 +319,10 @@ static int add_direct_chain(struct mlx5_vdpa_dev *mvdev, u64 start, u64 size, u8
 	while (size) {
 		sz = (u32)min_t(u64, MAX_KLM_SIZE, size);
 		dmr = kzalloc(sizeof(*dmr), GFP_KERNEL);
-		if (!dmr)
+		if (!dmr) {
+			err = -ENOMEM;
 			goto err_alloc;
+		}
 
 		dmr->start = st;
 		dmr->end = st + sz;