drm/imx: Remove imx_drm_crtc_id()

There is no one calling imx_drm_crtc_id() and it is just a simple
wrapper of drm_crtc_index() without doing any thing fancy - the
drivers may call drm_crtc_index() directly.  So, let's remove the
wrapper.
Signed-off-by: Liu Ying <gnuiyl@gmail.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

drivers/gpu/drm/imx/imx-drm-core.c

@@ -58,12 +58,6 @@ static int legacyfb_depth = 16;
 module_param(legacyfb_depth, int, 0444);
 #endif
 
-unsigned int imx_drm_crtc_id(struct imx_drm_crtc *crtc)
-{
-	return drm_crtc_index(crtc->crtc);
-}
-EXPORT_SYMBOL_GPL(imx_drm_crtc_id);
-
 static void imx_drm_driver_lastclose(struct drm_device *drm)
 {
 	struct imx_drm_device *imxdrm = drm->dev_private;

drivers/gpu/drm/imx/imx-drm.h

@@ -13,8 +13,6 @@ struct drm_plane;
 struct imx_drm_crtc;
 struct platform_device;
 
-unsigned int imx_drm_crtc_id(struct imx_drm_crtc *crtc);
-
 struct imx_crtc_state {
 	struct drm_crtc_state			base;
 	u32					bus_format;