RDMA/qib: Remove useless qib_read_ureg() function

Fix the following clang warning:

drivers/infiniband/hw/qib/qib_iba7322.c:803:19: warning: unused function 'qib_read_ureg' [-Wunused-function].

Link: https://lore.kernel.org/r/1618305063-29007-1-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>