usbhid(4): Increase probe priority to BUS_PROBE_DEFAULT + 1

usbhid(4) vs other USB HID drivers precedence is determined by
hw.usb.usbhid.enable loader tunable and HID quirk subsystem rather
than by device_probe() return value. Raise priority high enough to
always give usbhid(4) a possible chance to attach.

Fixes usbhid(4) attachment on USB device hotplug.

Reported by: Ivan Quitschal <tezeka_AT_hotmail_DOT_com>
MFC after: 1 week