RDMA/irdma: Make irdma_create_mg_ctx return a void

The function irdma_create_mg_ctx always returns 0, so make it void and
delete the return value check.

Link: https://lore.kernel.org/r/20220224182832.3896686-1-yanjun.zhu@linux.dev


Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Acked-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>