[MTD] OneNAND: Remove line of code that was meant to be deleted in OOB_AUTO

- Iterations of the patch to add oob auto-placement support to OneNAND left a line of code that was meant to have been deleted.
- read mtd->oobsize in onenand_transfer_auto_oob to optimized memcpy

Signed-off-by: Adrian Hunter <ext-adrian.hunter@nokia.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>