video: fbdev: au1200fb: Fix error handling path

Rewrite the exit path based on 'au1200fb_drv_remove()'.
We can safely iterate for all already handled planes. Even if not
completely initialized, the functions that are called will silently accept
the 'fb_info' structure that is passed.

As soon as we find a NULL in the '_au1200fb_infos' array, we know that we
have released all what we needed to release. So we can 'break'.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>