mtd: nand: don't break long print messages

This follows Chapter 2 of Linux's CodingStyle:
> However, never break user-visible strings such as printk messages,
> because that breaks the ability to grep for them.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>