osmo_libusb: Print log message on libusb initialization error

Change-Id: I2ac56e378e1279e7e333d93e54cd7a182d76498d
diff --git a/src/usb/osmo_libusb.c b/src/usb/osmo_libusb.c
index 79a8fc3..c5ea507 100644
--- a/src/usb/osmo_libusb.c
+++ b/src/usb/osmo_libusb.c
@@ -740,8 +740,10 @@
 	int rc;
 
 	rc = libusb_init(pluctx);
-	if (rc != 0)
+	if (rc != 0) {
+		LOGP(DLUSB, LOGL_ERROR, "Error initializing libusb: %s\n", libusb_strerror(rc));
 		return rc;
+	}
 
 	if (pluctx)
 		luctx = *pluctx;