UBI: fix EBADMSG handling

'ubi_io_read_data()' may return EBADMSG in case of an ECC error,
and we should not panic because of this. We have CRC32 checksum
and may check the data. So just ignore the EBADMSG error.

This patch also fixes a minor spelling error at the same time.

Signed-off-by: Zoltan Sogor <weth@inf.u-szeged.hu>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>