f2fs: avoid unneeded SetPageUptodate in f2fs_write_end

We have already set page update in ->write_begin, so we should remove redundant
SetPageUptodate in ->write_end.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>