f2fs: revive F2FS_IOC_ABORT_VOLATILE_WRITE

F2FS_IOC_ABORT_VOLATILE_WRITE was used to abort a atomic write before.
However it was removed accidentally. So revive it by changing the name,
since volatile write had gone.

Signed-off-by: Daeho Jeong <daehojeong@google.com>
Fiexes: 7bc155fe

("f2fs: kill volatile write support")
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>