RDMA/iwcm: Use list_first_entry() where appropriate

Improve source code readability by using list_first_entry() where appropriate.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20240605145117.397751-2-bvanassche@acm.org


Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Signed-off-by: Leon Romanovsky <leon@kernel.org>