rockchip: i2c: don't sent stop bit after each message

That's not correct and it breaks SMBUS-style reads and and writes for
some chips (e.g. SYR82X/SYR83X).

Stop bit should be sent only after the last message.

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>