mtd: OneNAND: do not use DMA if oops in progress

Otherwise we may hang if we are called from panic() through mtdoops.

Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>