staging: unisys: visorbus: add static declarations

Add static declarations to statisfy sparse warnings in:
  drivers/staging/unisys/visorbus/visorbus_main.c

  warning: symbol 'visorbus_debug' was not declared
  warning: symbol 'visorbus_forcematch' was not declared
  warning: symbol 'visorbus_forcenomatch' was not declared
  warning: symbol 'visorbus_devicetest' was not declared
  warning: symbol 'visorbus_debugref' was not declared
  warning: symbol 'visorbus_bus_groups' was not declared
  warning: symbol 'devmajorminor_create_file' was not declared
  warning: symbol 'devmajorminor_remove_file' was not declared
  warning: symbol 'devmajorminor_remove_all_files' was not declared
  warning: symbol 'unregister_devmajorminor_attributes' was not declared

Signed-off-by: Drew Fustini <pdp7pdp7@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>