usb: use only usb_devinfo() in device_set_usb_desc()

device_set_usb_desc() first tries to fetch device information through
the iInterface descriptor, otherwise it falls back to usb_devinfo().
Since usb_devinfo() is both guaranteed to work, and is more verbose, get
rid of the initial iInterface attempt.

Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
Reviewed by: imp, markj
Differential Revision: https://reviews.freebsd.org/D43383