altos/lpc: Reset less of the device on USB reset.

This leaves most of the device configured across USB reset, which
appears to help when sending a IN reply to the first SETUP packet;
without this change, the IN reply would always get a length of 0,
which is fine for SET_ADDRESS, but not for GET_DESCRIPTOR_DEVICE,
which OS X appears to send before setting the address (go figure).

Signed-off-by: Keith Packard <keithp@keithp.com>