platform/x86: GPD pocket fan: Use a min-speed of 2 while charging

Newer versions of the GPD pocket BIOS set the fan-speed to 2 when a
charger gets plugged in while the device is off. Mirror this in our
fan driver and use a minimum speed of 2 while charging,

Cc: James <kernel@madingley.org>
Suggested-by: James <kernel@madingley.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>