USB: cdc-acm: signedness fix

Fix bogus assignment of "unsigned char *" to "char *":  preserve
unsignedness.  These values are used directly as descriptor lengths
when iterating through the buffer, so this *could* cause oddness
that potentially includes oopsing.  (IMO not likely, except as
part of a malicious device...)

Fix the bogus warning in CDC ACM which highlighted this problem
(by showing a negative descriptor type).  It uses the undesirable
legacy err() for something that's not even an error; switch to
use dev_dbg, and show descriptor types in hex notation to match
the convention for such codes.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/class/cdc-acm.c

@@ -804,7 +804,7 @@ static int acm_probe (struct usb_interface *intf,
 {
 	struct usb_cdc_union_desc *union_header = NULL;
 	struct usb_cdc_country_functional_desc *cfd = NULL;
-	char *buffer = intf->altsetting->extra;
+	unsigned char *buffer = intf->altsetting->extra;
 	int buflen = intf->altsetting->extralen;
 	struct usb_interface *control_interface;
 	struct usb_interface *data_interface;
@@ -881,9 +881,13 @@ static int acm_probe (struct usb_interface *intf,
 				if ((call_management_function & 3) != 3)
 					err("This device cannot do calls on its own. It is no modem.");
 				break;
-				
 			default:
-				err("Ignoring extra header, type %d, length %d", buffer[2], buffer[0]);
+				/* there are LOTS more CDC descriptors that
+				 * could legitimately be found here.
+				 */
+				dev_dbg(&intf->dev, "Ignoring descriptor: "
+						"type %02x, length %d\n",
+						buffer[2], buffer[0]);
 				break;
 			}
 next_desc: