drm/mediatek: Use ERR_CAST instead of ERR_PTR(PTR_ERR())

Use ERR_CAST inlined function instead of ERR_PTR(PTR_ERR(...)).

drivers/gpu/drm/mediatek/mtk_drm_gem.c:223:9-16: WARNING: ERR_CAST can be used with mtk_gem
Generated by: scripts/coccinelle/api/err_cast.cocci

Signed-off-by: Vasyl Gomonovych <gomonovych@gmail.com>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: CK Hu <ck.hu@mediatek.com>

drivers/gpu/drm/mediatek/mtk_drm_gem.c

@@ -220,7 +220,7 @@ struct drm_gem_object *mtk_gem_prime_import_sg_table(struct drm_device *dev,
 	mtk_gem = mtk_drm_gem_init(dev, attach->dmabuf->size);
 
 	if (IS_ERR(mtk_gem))
-		return ERR_PTR(PTR_ERR(mtk_gem));
+		return ERR_CAST(mtk_gem);
 
 	expected = sg_dma_address(sg->sgl);
 	for_each_sg(sg->sgl, s, sg->nents, i) {