mlxsw: spectrum: Fix check for IS_ERR() instead of NULL

mlxsw_afa_block_create() doesn't return error pointers, it returns NULL
on error.

Fixes: 0e14c777 ("mlxsw: spectrum: Add the multicast routing hardware logic")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Acked-by: NYotam Gigi <yotamg@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/spectrum_mr_tcam.c

@@ -239,8 +239,8 @@ mlxsw_sp_mr_tcam_afa_block_create(struct mlxsw_sp *mlxsw_sp,
 	int err;
 
 	afa_block = mlxsw_afa_block_create(mlxsw_sp->afa);
-	if (IS_ERR(afa_block))
-		return afa_block;
+	if (!afa_block)
+		return ERR_PTR(-ENOMEM);
 
 	err = mlxsw_afa_block_append_counter(afa_block, counter_index);
 	if (err)