i2c: Document the message size limit

i2c_master_send & i2c_master_recv do not support more than 64 kb
transfer, since msg.len is u16.

Signed-off-by: Zhangfei Gao <zgao6@marvell.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

include/linux/i2c.h

@@ -53,6 +53,7 @@ struct i2c_board_info;
  * on a bus (or read from them). Apart from two basic transfer functions to
  * transmit one message at a time, a more complex version can be used to
  * transmit an arbitrary number of messages without interruption.
+ * @count must be be less than 64k since msg.len is u16.
  */
 extern int i2c_master_send(struct i2c_client *client, const char *buf,
 			   int count);