Fix byte-reversal of language ID in string descriptor.

The language id of String Descriptors in usb mouse is
0x0904, while the spec require 0x0409 (English - United States)

Submitted by: Wanpeng Qian
Reviewed by: grehan
Approved by: grehan (bhyve)
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D26472