RDMA/cxgb4: Fix missing error code in create_qp()

RDMA/cxgb4: Fix missing error code in create_qp()

The error code is missing in this code scenario so 0 will be returned. Add
the error code '-EINVAL' to the return value 'ret'.

Eliminates the follow smatch warning:

drivers/infiniband/hw/cxgb4/qp.c:298 create_qp() warn: missing error code 'ret'.

Link: https://lore.kernel.org/r/1622545669-20625-1-git-send-email-jiapeng.chong@linux.alibaba.com
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>