i2c: mediatek: Fixup i2c ack error interrupt handling

When occur i2c ack error, i2c controller generate two interrupts,
first is the ack error interrupt, then the complete interrupt.
i2c interrupt handler should keep the two interrupt value, and only
call complete() for the complete interrupt.

Signed-off-by: Liguo Zhang <liguo.zhang@mediatek.com>
Signed-off-by: Eddie Huang <eddie.huang@mediatek.com>
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>