mtd: onenand: fix omap2 code to handle cache program feature

Some fixes are introduced into omap2 code to handle errors when
cache program feature is used.

Signed-off-by: Roman Tereshonkov <roman.tereshonkov@nokia.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>