WUSB: remove an unnused variable

The "wusb_cap_descr_default" is never used.  GCC doesn't complain about
it because we have that line ".bLength = sizeof(wusb_cap_descr_default)"
inside the definition itself.  Clang complains though.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>