IB/mthca: fix return value of error branch in mthca_init_cq()

We return 'err' in the error branch, but this variable may be set as zero
by the above code. Fix it by setting 'err' as a negative value before we
goto the error label.

Fixes: 74c2174e ("IB uverbs: add mthca user CQ support")
Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Link: https://lore.kernel.org/r/1605837422-42724-1-git-send-email-wangxiongfeng2@huawei.com


Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>