[MTD] [OneNAND] Do not stop reading for ECC errors

When an ECC error occurs, the read should be completed
anyway before returning -EBADMSG.  Returning -EBADMSG
straight away is incorrect.

Signed-off-by: Adrian Hunter <ext-adrian.hunter@nokia.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>