wmt(4): Fix regression introduced in r337289

r337289 has a side effect of reducing usb frame 0 buffer size down to
touch report size. That broke some devices e.g. "Raydium Touch System"
which are capable of generating non-touch frames of bigger length.
Fix it with enlarging frame 0 buffer up to internal wmt(4) buffer size.

Reported by: Roberto Fernandez Cueto <roberfern@gmail.com>
Tested by: Roberto Fernandez Cueto <roberfern@gmail.com>
Approved by: re (gjb)
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D16772