Darwin: Fix warning: comparison between signed and unsigned
Darwin: Fix warning: comparison between signed and unsigned

libusbx.git commit c5c6b0e69a13786e48b2b6254c8e5458dc6716cc

tenderlove/libusb,dasdeepak/libusb,tenderlove/libusb,legege/libusb,ashima/libusb,legege/libusb,bert/libusb,ashima/libusb,hjelmn/libusb-darwin,bert/libusb,legege/libusb,dasdeepak/libusb,ashima/libusb,dasdeepak/libusb,hjelmn/libusb-darwin