drm/xe: Convert mem_access_if_ongoing to direct xe_pm_runtime_get_if_active

drm/xe: Convert mem_access_if_ongoing to direct xe_pm_runtime_get_if_active

Now that assert_mem_access is relying directly on the pm_runtime state
instead of the counters, there's no reason why we cannot use
the pm_runtime functions directly.

Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240417203952.25503-8-rodrigo.vivi@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>