drm/exynos: fix a warning message

The "ret = regmap_write()" assignment was missing so this error message
is never printed.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_mic.c

@@ -129,7 +129,7 @@ static void mic_set_path(struct exynos_mic *mic, bool enable)
 	} else
 		val &= ~(MIC0_RGB_MUX | MIC0_I80_MUX | MIC0_ON_MUX);
 
-	regmap_write(mic->sysreg, DSD_CFG_MUX, val);
+	ret = regmap_write(mic->sysreg, DSD_CFG_MUX, val);
 	if (ret)
 		DRM_ERROR("mic: Failed to read system register\n");
 }