ITE: drivers/i2c/i2c_ite_enhance: Fix I2C dump messages

The ISR for CQ mode was unconditionally writing into the I2C message
buffer for all transfer types. The correct data was transferred on the
I2C interface, but the clobber caused CONFIG_I2C_LOG_LEVEL_DBG to
display incorrect data for I2C writes.

This change will also help performance of large I2C write transactions.

Signed-off-by: Keith Short <keithshort@google.com>