Remove infinite recursion in OpenBSD backend

`usbi_dbg` calls `usbi_backend.clock_gettime`, so `obsd_clock_gettime` should
not call `usbi_dbg`

Signed-off-by: Nathan Hjelm <hjelmn@google.com>
diff --git a/libusb/os/openbsd_usb.c b/libusb/os/openbsd_usb.c
index a39c0f2..7e8197d 100644
--- a/libusb/os/openbsd_usb.c
+++ b/libusb/os/openbsd_usb.c
@@ -519,8 +519,6 @@
 int
 obsd_clock_gettime(int clkid, struct timespec *tp)
 {
-	usbi_dbg("clock %d", clkid);
-
 	if (clkid == USBI_CLOCK_REALTIME)
 		return clock_gettime(CLOCK_REALTIME, tp);