usb/isp1760: Remove false error printout

This removes the "qh is 0" printout. qh == NULL if the urb has
been unlinked, so this condition is normal.

Signed-off-by: Arvid Brodin <arvid.brodin@enea.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>