staging: unisys: visorbus: Convert visorchannel_signalinsert() return val

Per Documentation/CodingStyle, function names that convey an action or an
imperative command should return an integer. This commit converts the
visorbus API function, visorchannel_signalinsert(), to returning integer
values. All uses of this function are updated accordingly.

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