drm/i915/ttm: tweak priority hint selection

For some reason we are selecting PRIO_HAS_PAGES when we don't have
mm.pages, and vice versa.

v2(Thomas):
  - Add missing fixes tag

Fixes: 213d5092 ("drm/i915/ttm: Introduce a TTM i915 gem object backend")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220209111652.468762-1-matthew.auld@intel.com

drivers/gpu/drm/i915/gem/i915_gem_ttm.c

@@ -840,11 +840,9 @@ void i915_ttm_adjust_lru(struct drm_i915_gem_object *obj)
 	} else if (obj->mm.madv != I915_MADV_WILLNEED) {
 		bo->priority = I915_TTM_PRIO_PURGE;
 	} else if (!i915_gem_object_has_pages(obj)) {
-		if (bo->priority < I915_TTM_PRIO_HAS_PAGES)
-			bo->priority = I915_TTM_PRIO_HAS_PAGES;
+		bo->priority = I915_TTM_PRIO_NO_PAGES;
 	} else {
-		if (bo->priority > I915_TTM_PRIO_NO_PAGES)
-			bo->priority = I915_TTM_PRIO_NO_PAGES;
+		bo->priority = I915_TTM_PRIO_HAS_PAGES;
 	}
 
 	ttm_bo_move_to_lru_tail(bo, bo->resource, NULL);