i2c-core: Use per-adapter userspace device lists

Using a single list for all userspace devices leads to a dead lock
on multiplexed buses in some circumstances (mux chip instantiated
from userspace). This is solved by using a separate list for each
bus segment.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Michael Lawnick <ml.lawnick@gmx.de>
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 0a5da63..6ed1d59 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -355,6 +355,8 @@
 	int nr;
 	char name[48];
 	struct completion dev_released;
+
+	struct list_head userspace_clients;
 };
 #define to_i2c_adapter(d) container_of(d, struct i2c_adapter, dev)