f2fs: remove unneeded page uptodate check/set

This patch remove unneeded page uptodate check/set in
f2fs_vm_page_mkwrite, which already done in set_page_dirty.

Signed-off-by: Yunlei He <heyunlei@oppo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>