drm/xe: ensure correct access_put ordering

Only call access_put after dropping the forcewake. In theory the device
could suspend, but really we want to start asserting that we have a
mem_access.ref when touching mmio.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>