drm/imx: imx-ldb: fix channel->edid memleak

If edid was allocated during bind, it must be freed again during unbind.

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>