i2c: Add support for nested i2c bus locking

This patch adds the 'level' field into the i2c_adapter structure, which is 
used to represent the 'logical' level of nesting for the purposes of 
lockdep. This field is then used in the i2c_transfer() function, to 
acquire the per-adapter bus_lock with correct nesting level.

Signed-off-by: Jiri Kosina <jikos@jikos.cz>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

include/linux/i2c.h

@@ -216,6 +216,7 @@ struct i2c_adapter {
 	int (*client_unregister)(struct i2c_client *);
 
 	/* data fields that are valid for all devices	*/
+	u8 level; 			/* nesting level for lockdep */
 	struct mutex bus_lock;
 	struct mutex clist_lock;