IB/hfi1: Remove atomic operations for SDMA_REQ_HAVE_AHG bit

The AHG index is only accessed in the request call
from user space, so there's no need for atomic semantics.
Replace atomic operations for SDMA_REQ_HAVE_AHG bit
with a test of the AHG index.

Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Sebastian Sanchez <sebastian.sanchez@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>