RDMA/mlx5: Remove not-used IB_FLOW_SPEC_IB define

IB_FLOW_SPEC_IB is not used in mlx5 and can be deleted.

Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Link: https://lore.kernel.org/r/20221208101954.687960-1-yanjun.zhu@intel.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>