Staging: most: hdm-usb/hdm_usb.c. Fix "missing static keyword" warnings

This is a patch to the most/hdm-usb/hdm_usb.c file. It
makes several local functions and structures static to prevent global
visibility.

Signed-off-by: Adrian Remonda <adrianremonda@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>