IB/hfi1: Fix hard lockup due to not using save/restore spin lock

Commit b9b06cb6
("IB/hfi1: Fix missing lock/unlock in verbs drain callback")
added a spin lock.

Unfortunately, the new lock code can be called from a base
level interrupt state, and an interrupt that can get stacked
will attempt to get the same lock.

Fix by using the flag save/restore spin lock variation.

Cc: stable@vger.kernel.org # 4.6+
Reviewed-by: Sebastian Sanchez <sebastian.sanchez@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>