staging: usbip: removed unnecessary if-else-statements

In each if-else case "return" is called. This is why
these if-else-statements are useless. Removing them
improves understanding and readability.

Signed-off-by: Kurt Kanzenbach <ly80toro@cip.cs.fau.de>
Signed-off-by: Stefan Reif <ke42caxa@cip.cs.fau.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>