staging: usbip: Fix build with --with-tcp-wrappers
staging: usbip: Fix build with --with-tcp-wrappers

With --with-tcp-wrappers=no specified, the build system reset LIBS to
the empty string and thus fails to link against libsysfs.

Signed-off-by: Dominik Paulus <36ca848addc8fd5f5f36084e024a20c0f1ca6071@fau.de>
Signed-off-by: Tobias Polzer <63da45749bbfb98bea0c3421c5b4b5537df462cd@fau.de>
Signed-off-by: Greg Kroah-Hartman <4645f7897fd33786a2ee1264d590b3c400559d85@linuxfoundation.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs