The problem is that call to libusb_get_descriptor() is defined as taking a void* for the buf parameter:

int libusb_get_descriptor(
  void *dev, unsigned char type, unsigned char index, void *buf, int s
+ize
)
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But the typemap for that is void *            T_PTR, and that translates as

T_PTR     $var = INT2PTR($type,SvIV($arg)).

Ie. it is expecting the pointer to be passed as an integer in the IV slot. Hence the "argument isn't numeric".

In order to pass a buffer in the PV slot, as the perl code is doing, the type should be one of those that translates to

T_PV    $var = ($type)SvPV_nolen($arg).

Eg. char *            T_PV

There seem to be several of the functions that make this error.