mtd: FSMC NAND remove PARTITION macro and fix compile noise

This removes the PARTITION macro that David didn't like and also
removes a local variable that was dangling unused in some #ifdefs
by being a bit more clever.

Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>