i2c-cht-wc: Ack read irqs after reading the data register

Testing has shown that writing 1 to clear the read-complete irq does
not work until the data register has been read first.

This commit fixes the driver to read the data register first, halving the
amount of interrupts in most cases since we mostly read on this i2c bus.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>