Add LIBUSB_CALL where needed to avoid warnings such as the following:
In file included from src/hardware/hantek-dso/api.c:34:0:
src/hardware/hantek-dso/dso.h:212:13:
note: expected 'libusb_transfer_cb_fn' but argument is of type 'void (*)(struct libusb_transfer *)'
SR_PRIV int dso_get_channeldata(const struct sr_dev_inst *sdi,
^
From sigrok's point of view, this analyzer has two differences:
* It does not require uploading the firmware.
* It returns garbage in some registers used for sanity checks.
Saleae's software ignores that garbage; sigrok only does if it
specifically detects the mcupro clone.