staging: usbip: remove unnecessary braces

This patch fixes the following checkpatch warning:
-WARNING: braces {} are not necessary for any arm of this statement

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