staging: unisys: visorbus: my_device_destroy add error handling

Add the proper error handling to my_device_destroy so it can be send
back up the stack for further error reporting.

Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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>