[MTD] NAND: Fix typo in mtd/nand/ts7250.c

I was unable to compile ts7250.c after your refactor commit,
it's a typo probably.

-- ynezz

From: Petr Stetiar <ynezz@true.cz>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>