f2fs: Remove usage of list iterator pas the loop for list_move_tail()

In preparation to limit the scope of a list iterator to the list
traversal loop, the usage of the list iterator variable 'next' should
be avoided past the loop body [1].

Instead of calling list_move_tail() on 'next' after the loop, it is
called within the loop if the correct location was found.
After the loop it covers the case if no location was found and it
should be inserted based on the 'head' of the list.

Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/


Signed-off-by: Jakob Koschel <jakobkoschel@gmail.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>