drm/i915: use gtt_get_size() instead of open coding it

Signed-off-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 0b09361..35ecabc 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1565,6 +1565,8 @@
 void i915_gem_release(struct drm_device *dev, struct drm_file *file);
 
 uint32_t
+i915_gem_get_gtt_size(struct drm_device *dev, uint32_t size, int tiling_mode);
+uint32_t
 i915_gem_get_gtt_alignment(struct drm_device *dev, uint32_t size,
 			    int tiling_mode, bool fenced);