drm/vc4: Fix handling of a pm_runtime_get_sync() success case.

If the device was already up, a 1 is returned instead of 0.  We were
erroring out, leading the 3D driver to sometimes fail at screen
initialization (generally with ENOENT returned to it).

Signed-off-by: Eric Anholt <eric@anholt.net>
Fixes: af713795c59f ("drm/vc4: Add a getparam ioctl for getting the V3D identity regs.")

drivers/gpu/drm/vc4/vc4_drv.c

@@ -57,21 +57,21 @@ static int vc4_get_param_ioctl(struct drm_device *dev, void *data,
 	switch (args->param) {
 	case DRM_VC4_PARAM_V3D_IDENT0:
 		ret = pm_runtime_get_sync(&vc4->v3d->pdev->dev);
-		if (ret)
+		if (ret < 0)
 			return ret;
 		args->value = V3D_READ(V3D_IDENT0);
 		pm_runtime_put(&vc4->v3d->pdev->dev);
 		break;
 	case DRM_VC4_PARAM_V3D_IDENT1:
 		ret = pm_runtime_get_sync(&vc4->v3d->pdev->dev);
-		if (ret)
+		if (ret < 0)
 			return ret;
 		args->value = V3D_READ(V3D_IDENT1);
 		pm_runtime_put(&vc4->v3d->pdev->dev);
 		break;
 	case DRM_VC4_PARAM_V3D_IDENT2:
 		ret = pm_runtime_get_sync(&vc4->v3d->pdev->dev);
-		if (ret)
+		if (ret < 0)
 			return ret;
 		args->value = V3D_READ(V3D_IDENT2);
 		pm_runtime_put(&vc4->v3d->pdev->dev);