xfs_repair: fix array overrun in do_inode_prefetch

xfs_repair: fix array overrun in do_inode_prefetch

Coverity spotted this:

do_inode_prefetch() does a while loop, creating queues:

        for (i = 0; i < thread_count; i++) {
		...
		create_work_queue(&queues[i], mp, 1);
		...
	}

and then does this to wait for them all to complete:

	for (; i >= 0; i--)
		destroy_work_queue(&queues[i]);

But we leave the first for loop with (i == thread_coun)t, and
the second one will try to index queues[] one past the end.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>