staging: unisys: visorhba: switch success handling to error handling

Addresses code audit feeback to switch from success handling to error
handling in visorhba_main.c/process_disk_notify().

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>