libusb0: return oocd error values

libusb0: return oocd error values

Commit d1b74376336814266236054f925a9964b87dd8a5 fixes libusb1 to
return OpenOCD error values instead of negative errors in Linux
kernel's style.
The same fix should be applied to libusb0 too.

Fix return value of libusb0 to uniform it to OpenOCD style.

Change-Id: I68478c29c91c6be720074f58c432fe51477e03ed
Fixes: d1b743763368 ("libusb: return oocd error values")
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/4698
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>