drm/i915: Use the i915_vma_flush_writes helper

We can use the existing helper in flush_write_domain() and save some lines
of code.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230721130741.1306563-1-tvrtko.ursulin@linux.intel.com

Author: tursulin

drivers/gpu/drm/i915/gem/i915_gem_domain.c

@@ -68,10 +68,8 @@ flush_write_domain(struct drm_i915_gem_object *obj, unsigned int flush_domains)
 	switch (obj->write_domain) {
 	case I915_GEM_DOMAIN_GTT:
 		spin_lock(&obj->vma.lock);
-		for_each_ggtt_vma(vma, obj) {
-			if (i915_vma_unset_ggtt_write(vma))
-				intel_gt_flush_ggtt_writes(vma->vm->gt);
-		}
+		for_each_ggtt_vma(vma, obj)
+			i915_vma_flush_writes(vma);
 		spin_unlock(&obj->vma.lock);
 
 		i915_gem_object_flush_frontbuffer(obj, ORIGIN_CPU);