mtd: nftl: clean up indentation, remove extraneous tabs

The hunk of code is indented too much by one level, fix this by
removing the extraneous tabs. Also terminate block comment using
the recommended coding style to clean up checkpatch warning.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>