IB/hfi1: Fix bug that blocks process on exit after port bounce

During the processing of a user SDMA request, if there was an
error before the request counter was increased, the state of
the packet queue could be updated incorrectly, causing the
counter to underflow. As the result, the process could get
stuck later since the counter could never get back to 0.

This patch adds a condition to guard the packet queue update
so that the counter is only decreased if it has been increased
before the error happens.

Reviewed-by: Mitko Haralanov <mitko.haralanov@intel.com>
Signed-off-by: Jianxin Xiong <jianxin.xiong@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>