staging: vt6656: Fix CARDvCalculateOFDMRParameter static warning

Fix  warning: symbol 'CARDvCalculateOFDMRParameter' was not declared. Should it be static?

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>