staging: unisys: visorbus: renamed functions like *_bus_instance to match driver namespace

Renamed functions
* create_bus_instance() to visorbus_create_instance()
* remove_bus_instance() to visorbus_remove_instance()

Signed-off-by: Sameer Wadgaonkar <sameer.wadgaonkar@unisys.com>
Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David Kershner <david.kershner@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>