pkg-config checks libgphoto2 that needs libgphoto2_port (both provided by libgphoto2-dev package). libgphoto2-port0 binary package depends on libusb-0.1-4 binary package but libgphoto2-dev DOESN'T depend on libusb-dev. pkg-config check of libgphoto2_port.pc fails because it can't find libusb.pc.
So it is a problem in libgphoto2-dev package not depending on libusb-dev, I think. If someone confirms this, please open a bug in libgphoto2 package.
Found it! ;-)
pkg-config checks libgphoto2 that needs libgphoto2_port (both provided by libgphoto2-dev package). libgphoto2-port0 binary package depends on libusb-0.1-4 binary package but libgphoto2-dev DOESN'T depend on libusb-dev. pkg-config check of libgphoto2_port.pc fails because it can't find libusb.pc.
So it is a problem in libgphoto2-dev package not depending on libusb-dev, I think. If someone confirms this, please open a bug in libgphoto2 package.