hwrng: mtk - Use devm_pm_runtime_enable

Replace pm_runtime_enable with the devres-enabled version which
can trigger pm_runtime_disable.

Otherwise, the below appears during reload driver.

mtk_rng 1020f000.rng: Unbalanced pm_runtime_enable!

Fixes: 81d2b34 ("hwrng: mtk - add runtime PM support")
Cc: <stable@vger.kernel.org>
Suggested-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: Guoqing Jiang <guoqing.jiang@canonical.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/mtk-rng.c

@@ -142,7 +142,7 @@ static int mtk_rng_probe(struct platform_device *pdev)
 	dev_set_drvdata(&pdev->dev, priv);
 	pm_runtime_set_autosuspend_delay(&pdev->dev, RNG_AUTOSUSPEND_TIMEOUT);
 	pm_runtime_use_autosuspend(&pdev->dev);
-	pm_runtime_enable(&pdev->dev);
+	devm_pm_runtime_enable(&pdev->dev);
 
 	dev_info(&pdev->dev, "registered RNG driver\n");