drm/msm/dp: Fix platform_get_irq() check

The platform_get_irq() function returns negative error codes.  It never
returns zero.  Fix the check accordingly.

Fixes: 82c2a575 ("drm/msm/dp: tie dp_display_irq_handler() with dp driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/570755/
Link: https://lore.kernel.org/r/c12bb69b-d676-4345-9712-48aab48f2b48@moroto.mountainSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/msm/dp/dp_display.c

@@ -1168,9 +1168,9 @@ static int dp_display_request_irq(struct dp_display_private *dp)
 	struct platform_device *pdev = dp->dp_display.pdev;
 
 	dp->irq = platform_get_irq(pdev, 0);
-	if (!dp->irq) {
+	if (dp->irq < 0) {
 		DRM_ERROR("failed to get irq\n");
-		return -EINVAL;
+		return dp->irq;
 	}
 
 	rc = devm_request_irq(&pdev->dev, dp->irq, dp_display_irq_handler,