staging: vt6656: struct vnt_private remove dead code ldBmThreshold

ldBmThreshold was used in old function s_vCheckSensitivity which
had been disabled in orginal vendors code.

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