net/mlx5e: Fix unnecessary flow_block_cb_is_busy call

When call flow_block_cb_is_busy. The indr_priv is guaranteed to
NULL ptr. So there is no need to call flow_bock_cb_is_busy.

Fixes: 0d4fd02e ("net: flow_offload: add flow_block_cb_is_busy() and use it")
Signed-off-by: wenxu <wenxu@ucloud.cn>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>