staging: imx-drm: imx-tve: Check the return value of 'regulator_enable()'

Since commit c8801a8e (regulator: core: Mark all get and enable calls as
__must_check) we need to check the value returned by 'regulator_enable()'.

Do this check to get rid of the following build warning:

drivers/staging/imx-drm/imx-tve.c: In function 'imx_tve_probe':
drivers/staging/imx-drm/imx-tve.c:671:19: warning: ignoring return value of 'regulator_enable', declared with attribute warn_unused_result [-Wunused-result]
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/imx-drm/imx-tve.c

@@ -670,7 +670,9 @@ static int imx_tve_probe(struct platform_device *pdev)
 	tve->dac_reg = devm_regulator_get(&pdev->dev, "dac");
 	if (!IS_ERR(tve->dac_reg)) {
 		regulator_set_voltage(tve->dac_reg, 2750000, 2750000);
-		regulator_enable(tve->dac_reg);
+		ret = regulator_enable(tve->dac_reg);
+		if (ret)
+			return ret;
 	}
 
 	tve->clk = devm_clk_get(&pdev->dev, "tve");