f2fs: reorganize f2fs_vm_page_mkwrite
f2fs: reorganize f2fs_vm_page_mkwrite

Few things can be changed in the default mkwrite function
1) Make file_update_time at the start before acquiring any lock
2) the condition page_offset(page) >= i_size_read(inode) should be
 changed to page_offset(page) > i_size_read
3) Move wait_on_page_writeback.

Signed-off-by: Namjae Jeon <65d484aa1efdaf0ae258f87a04ed8ec8685cba3e@samsung.com>
Signed-off-by: Amit Sahrawat <45f453362837a515932de958af84a8a1577409ad@samsung.com>
Signed-off-by: Jaegeuk Kim <20424effba9d4aeeb410130c5f23aa328fa29e09@samsung.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs