hidapi: Use LIBUSB_LIBRARIES to link to libusb

[leoetlino]

Because we have an old-style find script that does not define a proper
CMake target for libusb, we need to use ${LIBUSB_LIBRARIES}
rather than "usb".

Ideally, we would fix the find script to define a target. However,
this issue breaks the fifoci-ogl-lin-mesa builder and I'd prefer it
to be fixed sooner rather than later.

[iwubcode]

Because we have an old-style find script that does not define a proper
CMake target for libusb, we need to use ${LIBUSB_LIBRARIES}
rather than "usb".

I'm fairly familiar with CMake but I don't know much about Dolphin's build system. I didn't realize we were exposing these to the find functionality. I assumed the add_library like defined here was good enough. Where do expose these external's to CMake's search path?

[leoetlino]

The issue isn't in our Externals CMakeLists.txt, but in FindLibUSB.cmake, which doesn't define a real CMake target.

[merryhime]

works locally, thanks (for reference the target is a stripped down AArch64 machine without libusb)