staging: unisys: include: iochannel.h: removed VISOR_VHBA_CHANNEL_SIGNATURE

VISOR_VHBA_CHANNEL_SIGNATURE is a redundant definition that points to
VISOR_CHANNEL_SIGNATURE. This replaces that definition with
VISOR_CHANNEL_SIGNATURE.

Signed-off-by: Alex Curtin <alexander.curtin@unisys.com>
Signed-off-by: David Kershner <david.kershner@unisys.com>
Reviewed-by: David Binder <david.binder@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>