imx-drm: imx-drm-core: fix error cleanup path for imx_drm_add_crtc()

imx_drm_add_crtc() was kfree'ing the imx_drm_crtc structure while
leaving it on the list of CRTCs.  Delete it from the list first.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>