usbopen page fault

[Arto Huusko <arto.huusko%pp2.inet.fi@localhost>]

-current kernel (from a few hours ago) crashes in usbopen with page
fault trap when starting pcscd daemon (which I guess uses /dev/ugen
or /dev/usb).

Trace is

usbopen
cdev_open
spec_open
VOP_OPEN
vn_open
sys_open

Faulting instruction is at usbopen+0x53 (amd64), and the instruction
is cmpb $0x1, 0x30(%rax). show registers in ddb shows rax is 0.
Possibly a mistake was made in some softc/device_t split?