GitLab

Commit 472ac475

 introduced
a possible regression by relying on the availability of
libusb_strerror(). There are libusb versions out there _not_
offering this function, which breaks compilation.

Introducing a separate helper function allows us to work around
this, refactor existing code and have more streamlined error
reporting - avoiding the message string retrieval where needed.
The usb_error() function can also optionally abort execution
with a given exit code.
Signed-off-by: Bernhard Nortmann <bernhard.nortmann@web.de>