drm/i915: Use i915_vma_offset() in intel_dpt_offset()

Replace the open coded vma mm node stuff in intel_dpt_offset()
with i915_vma_offset(). This will also include the VT-d guard
in the result. Granted that should always be 0 for DPT, but
it seems prudent to include that in our DPT vma offset check
anyway.

Reviewed-by: Jani Nikula <[e-mail]>
Signed-off-by: Ville Syrjälä <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/i915/display/intel_dpt.c

···
 
 u64 intel_dpt_offset(struct i915_vma *dpt_vma)
 {
-	return dpt_vma->node.start;
+	return i915_vma_offset(dpt_vma);
 }

drivers/gpu/drm/i915/display/intel_fb_pin.c

···
 		WARN_ON(plane_state->ggtt_vma == plane_state->dpt_vma);
 
 		/*
-		 * The DPT object contains only one vma, so
-		 * the VMA's offset within the DPT is always 0.
+		 * The DPT object contains only one vma, and there is no VT-d
+		 * guard, so the VMA's offset within the DPT is always 0.
 		 */
 		drm_WARN_ON(display->drm, intel_dpt_offset(plane_state->dpt_vma));
 	}