f2fs: remove the unused argument "sbi" of func destroy_fsync_dnodes()

As destroy_fsync_dnodes() is a simple list-cleanup func, so delete the unused
and unrelated f2fs_sb_info argument of it.

Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>