mtd: nand: Get rid of comments giving the file path inside the file itself

Some files add a comment giving the path of the file inside the Linux
tree, which is pretty useless since the reader had to find the file to
open it.

Getting rid of these comments will also allow us to easily move these
files around when needed.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>