f2fs: don't convert inline inode when inline_data option is disable

If inline_data option is disable, when truncating an inline inode with
size which is not exceed maxinum inline size, we should not convert
inline inode to regular one to avoid the overhead of synchronizing
conversion.

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