staging: unisys: visorbus: Convert macros to functions.

Several macros in visorchannel.c were doing complex arithmetic, converted
them to functions so that valid type checking could be done.

Signed-off-by: David Kershner <david.kershner@unisys.com>
Reviewed-by: Tim Sell <timothy.sell@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>