block: ioc_cgroup_changed() needs to be exported

With the ioc changed, ioc_cgroup_changed() can be used by modular
code. So ensure that it is exported.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-ioc.c

@@ -464,6 +464,7 @@ void ioc_cgroup_changed(struct io_context *ioc)
 	ioc_set_changed(ioc, ICQ_CGROUP_CHANGED);
 	spin_unlock_irqrestore(&ioc->lock, flags);
 }
+EXPORT_SYMBOL(ioc_cgroup_changed);
 
 static int __init blk_ioc_init(void)
 {