RDMA/irdma: Remove extra ret variable in favor of existing err

In the function irdma_reg_user_mr, err and ret exist. Actually,
one variable err is enough.

Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Link: https://lore.kernel.org/r/20230104064333.660344-1-yanjun.zhu@intel.com


Signed-off-by: Leon Romanovsky <leon@kernel.org>