Change log from v1:
o handle NULL pointer of grab_cache_page_write_begin() pointed by Chao Yu.
This patch refactors f2fs_convert_inline_data to check a couple of conditions
internally for deciding whether it needs to convert inline_data or not.
So, the new f2fs_convert_inline_data initially checks:
1) f2fs_has_inline_data(), and
2) the data size to be changed.
If the inode has inline_data but the size to fill is less than MAX_INLINE_DATA,
then we don't need to convert the inline_data with data allocation.
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>