In ramfs_truncate() "newchunks" denotes the number of chunks we
want to have after the call. We decrease that number while iterating
over the existing chunks and decrease it further with every newly
allocated chunk until "newchunks" is zero.
This is a bit hard to read. Instead we drop the decreasing while
iterating over existing chunks and increase "oldchunks" while allocating
until it reaches "newchunks".

This is mainly done to make the next patch easier.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>