HID: logitech-hidpp: do not hardcode very long report length

The HID++ spec says the following about the very long report length:
"n Bytes, depends on HID++ collection declaration".

Hardcoding this breaks talking to some HID++ devices over BlueTooth, since
they declare only 45 bytes data for the very long report, rather then the
hardcoded 63.

This commit fixes this by getting the actual report length from the
descriptors.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>