HID: logitech-hidpp: Silence protocol errors on newer lightspeed receivers

When logitech-hidpp tries to communicate with an unreachable device paired
to a 046d:c547 lightspeed receiver, the following message is printed to the
console:

hidpp_root_get_protocol_version: received protocol error 0x08

This occurs because this receiver returns 0x08 (HIDPP_ERROR_UNKNOWN_DEVICE)
when a device is unreachable, compared to 0x09 (HIDPP_ERROR_RESOURCE_ERROR)
that the older receivers return.

This patch silences this harmless error by treating
HIDPP_ERROR_UNKNOWN_DEVICE the same as HIDPP_ERROR_RESOURCE_ERROR
in hidpp_root_get_protocol_version().

There are other checks for HIDPP_ERROR_RESOURCE_ERROR found in
battery-related functions, however this receiver does not trigger them when
the device is disconnected.

Signed-off-by: Mavroudis Chatzilazaridis <mavchatz@protonmail.com>
Tested-by: Stuart Hayhurst <stuart.a.hayhurst@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>