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: Vasiliy Kulikov <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/radeon/radeon_irq.c

···
 		default:
 			DRM_ERROR("tried to enable vblank on non-existent crtc %d\n",
 				  crtc);
-			return EINVAL;
+			return -EINVAL;
 		}
 	} else {
 		switch (crtc) {
···
 		default:
 			DRM_ERROR("tried to enable vblank on non-existent crtc %d\n",
 				  crtc);
-			return EINVAL;
+			return -EINVAL;
 		}
 	}