JFS: call io_schedule() instead of schedule() to avoid deadlock

The introduction of Jens Axboe's explicit i/o plugging patches introduced a
deadlock in jfs.  This was caused by the process initiating I/O not
unplugging the queue before waiting on the commit thread.  The commit
thread itself was waiting for that I/O to complete.  Calling io_schedule()
rather than schedule() unplugs the I/O queue avoiding the deadlock, and it
appears to be the right function to call in any case.

Signed-off-by: Dave Kleikamp <shaggy@austin.ibm.com>