f2fs: clean up an unused parameter and assignment

This patch cleans up simple unnecessary codes.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

diff --cc fs/f2fs/dir.c
Simple merge

diff --cc fs/f2fs/f2fs.h
Simple merge

diff --cc fs/f2fs/namei.c
Simple merge

diff --cc fs/f2fs/node.c
Simple merge