HID cp2112: fix support for multiple gpiochips

In lk 5.11.0-rc2 connecting a USB based Silicon Labs HID to I2C
bridge evaluation board (CP2112EK) causes this warning:
  gpio gpiochip0: (cp2112_gpio): detected irqchip that is shared
       with multiple gpiochips: please fix the driver

Simply copy what other gpio related drivers do to fix this
particular warning: replicate the struct irq_chip object in each
device instance rather than have a static object which makes that
object (incorrectly) shared by each device.

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>