media: mtk-mdp: use IS_ERR to check return value of of_clk_get

Function of_clk_get() returns an ERR_PTR on failures. In file
mtk_mdp_commp.c, its return value is checked against NULL. Such checks
cannot prevent from accessing bad memory. This patch replaces the NULL
checks with IS_ERR checks.
Signed-off-by: NPan Bian <bianpan2016@163.com>
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/platform/mtk-mdp/mtk_mdp_comp.c

@@ -75,7 +75,7 @@ void mtk_mdp_comp_clock_on(struct device *dev, struct mtk_mdp_comp *comp)
 	}
 
 	for (i = 0; i < ARRAY_SIZE(comp->clk); i++) {
-		if (!comp->clk[i])
+		if (IS_ERR(comp->clk[i]))
 			continue;
 		err = clk_prepare_enable(comp->clk[i]);
 		if (err)
@@ -90,7 +90,7 @@ void mtk_mdp_comp_clock_off(struct device *dev, struct mtk_mdp_comp *comp)
 	int i;
 
 	for (i = 0; i < ARRAY_SIZE(comp->clk); i++) {
-		if (!comp->clk[i])
+		if (IS_ERR(comp->clk[i]))
 			continue;
 		clk_disable_unprepare(comp->clk[i]);
 	}