Fix libusb config descriptor leak
Fix libusb config descriptor leak

The descriptor received from libusb_get_active_config_descriptor was
never freed. Thus, when opening a channel repeatedly, more and more
memory was leaked (tested with valgrind).

LudovicRousseau/CCID,hiranotaka/ccid-scr331-nttcom,LudovicRousseau/CCID,LudovicRousseau/CCID,hiranotaka/ccid-scr331-nttcom,hiranotaka/ccid-scr331-nttcom,hiranotaka/ccid-scr331-nttcom