RDMA: Complete k[z|m|c]alloc-to-k[z|m]alloc_obj conversion

Commits bf4afc53b77a ("Convert 'alloc_obj' family to use the new default
GFP_KERNEL argument") and 69050f8d6d07 ("treewide: Replace kmalloc with
kmalloc_obj for non-scalar types") updated various k[z|m|c]alloc calls to their
k[z|m]alloc_obj counterparts.

This commit finalizes that transition within the RDMA subsystem.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>