Calculating the offset to a context is done several times throughout
the code.  Create a common inlined function for doing this
calculation.
Reviewed-by: NIra Weiny <ira.weiny@intel.com>
Signed-off-by: NMichael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: NDennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: NDoug Ledford <dledford@redhat.com>