[XFS] xfssyncd is responsible for flushing inode or device's data by

extracting the work from its queue. In addition, this processing also
decrement the inode's i_count. If there are any remaining works in queue
before this process terminates, we have unbalanced increment and decrement
of i_count. Thus it can cause assertion failure of vn_count. The fix
allows xyssyncd to process any remaining work before it is shutdown. 

SGI-PV: 945935
SGI-Modid: xfs-linux-melb:xfs-kern:203970a

Signed-off-by: Yingping Lu <yingping@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>