drm: Use IS_ERR() instead of IS_ERR_OR_NULL()

dev_pm_opp_find_freq_exact never return null but ERR_PTR(),so we
should use IS_ERR() to clarify and avoid compilation warnings.
Signed-off-by: Wang Qing <wangqing@vivo.com>
Link: https://lore.kernel.org/r/1604630714-6163-1-git-send-email-wangqing@vivo.comSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/adreno/a6xx_gmu.c

@@ -891,7 +891,7 @@ static void a6xx_gmu_set_initial_freq(struct msm_gpu *gpu, struct a6xx_gmu *gmu)
 	unsigned long gpu_freq = gmu->gpu_freqs[gmu->current_perf_index];
 
 	gpu_opp = dev_pm_opp_find_freq_exact(&gpu->pdev->dev, gpu_freq, true);
-	if (IS_ERR_OR_NULL(gpu_opp))
+	if (IS_ERR(gpu_opp))
 		return;
 
 	gmu->freq = 0; /* so a6xx_gmu_set_freq() doesn't exit early */
@@ -905,7 +905,7 @@ static void a6xx_gmu_set_initial_bw(struct msm_gpu *gpu, struct a6xx_gmu *gmu)
 	unsigned long gpu_freq = gmu->gpu_freqs[gmu->current_perf_index];
 
 	gpu_opp = dev_pm_opp_find_freq_exact(&gpu->pdev->dev, gpu_freq, true);
-	if (IS_ERR_OR_NULL(gpu_opp))
+	if (IS_ERR(gpu_opp))
 		return;
 
 	dev_pm_opp_set_opp(&gpu->pdev->dev, gpu_opp);