drm/imx: ipuv3-crtc: Return error if ipu_plane_init() fails for primary plane

For primary plane initialization failure cases, ipu_plane_init() may return
a pointer encoded by ERR_PTR(). So, we should bailout instead of using that
pointer blindly.

Signed-off-by: Liu Ying <Ying.Liu@freescale.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>