extern struct i2c_client *i2c_get_client(int,int,struct i2c_client *);
to make sure that client-struct is valid and that it is okay to access
the i2c-client.
- returns -EACCES if client doesn't allow use (default)
- returns -EBUSY if client doesn't allow multiple use (default) and
- usage_count >0 */
+ returns -ENODEV if client has gone in the meantime */
extern int i2c_use_client(struct i2c_client *);
extern int i2c_release_client(struct i2c_client *);