usb/if_mos.c: Fix incorrect SPDX ID

Fixes: 718cf2ccb995 (further adoption of SPDX)
MFC after: 3 days
Reviewed by: carlavilla, imp, mhorne
Approved by: carlavilla, mhorne (mentors)
Differential Revision: https://reviews.freebsd.org/D50374

(cherry picked from commit ca47411ea5e8a38ac1a9a29df25bc32ffcaa2904)