iichid(4): disable interrupt on suspend

Commit message of the identical change in Linux driver says:
"When an I2C HID device is powered off during system sleep, as a result
of removing its power resources (by the ACPI core) the interrupt line
might go low as well. This results inadvertent interrupts."

This change fixes suspend/resume on Asus S510UQ laptops.

While here add a couple of typo fixes as well as a slight change to the
iichid_attach() code to have the power_on flag set properly.

Submitted by: J.R. Oldroyd <jr_AT_opal_DOT_com>
Reviewed by: wulf
MFC after: 1 week