RDMA: remove useless condition in siw_create_cq()

Comparison of 'cq' with NULL is useless since
'cq' is a result of container_of and cannot be NULL
in any reasonable scenario.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 303ae1cd ("rdma/siw: application interface")
Link: https://lore.kernel.org/r/20220711151251.17089-1-strochuk@ispras.ru


Signed-off-by: Andrey Strachuk <strochuk@ispras.ru>
Acked-by: Bernard Metzler <bmt@zurich.ibm.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>