ACPI: Use ACPI companion to match only the first physical device

Commit 6ab34301 ("mfd: Add ACPI support") made the MFD subdevices
share the parent MFD ACPI companion if no _HID/_CID is specified for
the subdevice in mfd_cell description. However, since all the subdevices
share the ACPI companion, the match and modalias generation logic started
to use the ACPI companion as well resulting this:

  # cat /sys/bus/platform/devices/HID-SENSOR-200041.6.auto/modalias
  acpi:INT33D1:PNP0C50:

instead of the expected one

  # cat /sys/bus/platform/devices/HID-SENSOR-200041.6.auto/modalias
  platform:HID-SENSOR-200041

In other words the subdevice modalias is overwritten by the one taken from
ACPI companion. This causes udev not to load the driver anymore.

It is useful to be able to share the ACPI companion so that MFD subdevices
(and possibly other devices as well) can access the ACPI resources even if
they do not have ACPI representation in the namespace themselves.

An example where this is used is Minnowboard LPC driver that creates GPIO
as a subdevice among other things. Without the ACPI companion gpiolib is
not able to lookup the corresponding GPIO controller from ACPI GpioIo
resource.

To fix this, restrict the match and modalias logic to be limited to the
first (primary) physical device associated with the given ACPI comapnion.
The secondary devices will still be able to access the ACPI companion,
but they will be matched in a different way.

Fixes: 6ab34301 (mfd: Add ACPI support)
Reported-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>