drm/msm: fix returnvar.cocci warning

Fix the following coccicheck warning:
drivers/gpu/drm/msm/disp/mdp4/mdp4_kms.c:24:5-8: Unneeded variable:
"ret". Return "0" on line 75.
Signed-off-by: NGuo Zhengkui <guozhengkui@vivo.com>
Reviewed-by: NStephen Boyd <swboyd@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/483328/
Link: https://lore.kernel.org/r/20220425122223.7415-1-guozhengkui@vivo.comSigned-off-by: NDmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/msm/disp/mdp4/mdp4_kms.c

@@ -21,7 +21,6 @@ static int mdp4_hw_init(struct msm_kms *kms)
 	struct drm_device *dev = mdp4_kms->dev;
 	u32 dmap_cfg, vg_cfg;
 	unsigned long clk;
-	int ret = 0;
 
 	pm_runtime_get_sync(dev->dev);
 
@@ -72,7 +71,7 @@ static int mdp4_hw_init(struct msm_kms *kms)
 
 	pm_runtime_put_sync(dev->dev);
 
-	return ret;
+	return 0;
 }
 
 static void mdp4_enable_commit(struct msm_kms *kms)