mISDN: Fix wrong usage of flush_work_sync while holding locks

It is a bad idea to hold a spinlock and call flush_work_sync.
Move the workqueue cleanup outside the spinlock and use cancel_work_sync,
on closing the channel this seems to be the more correct function.
Remove the never used and constant return value of mISDN_freebchannel.

Signed-off-by: Karsten Keil <keil@b1-systems.de>
Cc: <stable@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/mISDNhw.h b/include/linux/mISDNhw.h
index d0752ec..9d96d5d 100644
--- a/include/linux/mISDNhw.h
+++ b/include/linux/mISDNhw.h
@@ -183,7 +183,7 @@
 				   unsigned short);
 extern int	mISDN_freedchannel(struct dchannel *);
 extern void	mISDN_clear_bchannel(struct bchannel *);
-extern int	mISDN_freebchannel(struct bchannel *);
+extern void	mISDN_freebchannel(struct bchannel *);
 extern int	mISDN_ctrl_bchannel(struct bchannel *, struct mISDN_ctrl_req *);
 extern void	queue_ch_frame(struct mISDNchannel *, u_int,
 			int, struct sk_buff *);