drm/exynos: remove ignoring return value warning in hdmi

The definition of regulator_bulk_enable is fixed with __must_check
and this causes following build warning.
warning: ignoring return value of 'regulator_bulk_enable',
declared with attribute warn_unused_result
This patch fixes to check return value of the function.
Signed-off-by: NSeung-Woo Kim <sw0312.kim@samsung.com>
Signed-off-by: NInki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_hdmi.c

@@ -1699,7 +1699,9 @@ static void hdmi_poweron(struct hdmi_context *hdata)
 
 	mutex_unlock(&hdata->hdmi_mutex);
 
-	regulator_bulk_enable(res->regul_count, res->regul_bulk);
+	if (regulator_bulk_enable(res->regul_count, res->regul_bulk))
+		DRM_DEBUG_KMS("failed to enable regulator bulk\n");
+
 	clk_enable(res->hdmiphy);
 	clk_enable(res->hdmi);
 	clk_enable(res->sclk_hdmi);