drm: radeon: fix error value sign

enable_vblank implementations should use negative result to indicate error.
radeon_enable_vblank() returns EINVAL in this case.  Change this to -EINVAL.
Signed-off-by: NVasiliy Kulikov <segoon@openwall.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_irq.c

@@ -76,7 +76,7 @@ int radeon_enable_vblank(struct drm_device *dev, int crtc)
 		default:
 			DRM_ERROR("tried to enable vblank on non-existent crtc %d\n",
 				  crtc);
-			return EINVAL;
+			return -EINVAL;
 		}
 	} else {
 		switch (crtc) {
@@ -89,7 +89,7 @@ int radeon_enable_vblank(struct drm_device *dev, int crtc)
 		default:
 			DRM_ERROR("tried to enable vblank on non-existent crtc %d\n",
 				  crtc);
-			return EINVAL;
+			return -EINVAL;
 		}
 	}