f2fs: move set_file_temperature into f2fs_new_inode

Since the file name has already passed to f2fs_new_inode(), let's
move set_file_temperature() into f2fs_new_inode().

Signed-off-by: Sheng Yong <shengyong@oppo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>