IB/qib: Remove redundant assignment to ret

Variable 'ret' is set to zero but this value is never read as it is
overwritten with a new value later on, hence it is a redundant assignment
and can be removed.

Clean up the following clang-analyzer warning:

drivers/infiniband/hw/qib/qib_sd7220.c:690:2: warning: Value stored to
'ret' is never read [clang-analyzer-deadcode.DeadStores]

Link: https://lore.kernel.org/r/1619692940-104771-1-git-send-email-yang.lee@linux.alibaba.com
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>