Don't print an error when libusb_cancel_transfer() fails with NOT_FOUND
Don't print an error when libusb_cancel_transfer() fails with NOT_FOUND

As stated in the documentation for libusb_cancel_transfer(),
LIBUSB_ERROR_NOT_FOUND is an expected return value for
libusb_cancel_transfer() under certain circumstances, so
printing an error every time this happens is undesirable.

Even more so because under Linux IOCTL_USBFS_DISCARDURB sets errno
to EINVAL when the kernel can't not find the urb in the kernel's
urbs-in-flight list, which means that the urb has already completed
at the host controller level but it has not necessarily been reaped
yet. IOW under Linux libusb_cancel_transfer() may yield a result of
LIBUSB_ERROR_NOT_FOUND *before* the transfer's callback has been
called! In conclusion there is no way for applications to avoid
calling libusb_cancel_transfer() on already completed transfers,
and these errors can and do happen frequently for some USB traffic.

Signed-off-by: Hans de Goede <9fa1be1a5b5729e4c6b404f34c9ce49ff4882fd8@redhat.com>

legege/libusb,SpecLad/libusb-android,dasdeepak/libusb,hjelmn/libusb-darwin,legege/libusb,SpecLad/libusb-android,ashima/libusb,ashima/libusb,hjelmn/libusb-darwin,bert/libusb,mojca/libusb_pico,ashima/libusb,legege/libusb,bert/libusb,Distrotech/libusb,tenderlove/libusb,Distrotech/libusb,tenderlove/libusb,Distrotech/libusb,dasdeepak/libusb,dasdeepak/libusb,mojca/libusb_pico,SpecLad/libusb-android