USB: cdc_acm: Silence "It is not a modem." error for pbLua devices

The pbLua console port is known to not be a modem, so it is
unnecessary to be told this when it is plugged in.

Add NOT_A_MODEM quirk to tell the driver that we know this already
and hence not to warn us, and mark the pbLua console port.

Signed-off-by: Julian Calaby <julian.calaby@gmail.com>
Cc: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/class/cdc-acm.h b/drivers/usb/class/cdc-acm.h
index 519eb63..4a8e87e 100644
--- a/drivers/usb/class/cdc-acm.h
+++ b/drivers/usb/class/cdc-acm.h
@@ -136,3 +136,4 @@
 #define NO_UNION_NORMAL			1
 #define SINGLE_RX_URB			2
 #define NO_CAP_LINE			4
+#define NOT_A_MODEM			8