hw/usb: Fix LGPL information in the file headers

hw/usb: Fix LGPL information in the file headers

It's either "GNU *Library* General Public version 2" or "GNU Lesser
General Public version *2.1*", but there was no "version 2.0" of the
"Lesser" library. So assume that version 2.1 is meant here.
Additionally, suggest that the user should have received a copy of
the LGPL, and not the GPL here.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-id: 1548254454-7659-1-git-send-email-thuth@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>