mtd: davinci nand: update clock naming

DaVinci clock support has been updated in mainline.
Update clock names accordingly.

Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>