[ALSA] usb-audio: add UM-1EX/UM-2EX information

Modules: USB generic driver

Add comments with information about UM-1EX/UM-2EX devices.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

sound/usb/usbquirks.h

@@ -294,7 +294,8 @@ YAMAHA_DEVICE(0x7010, "UB99"),
 	}
 },
 {
-	/* a later revision uses ID 0x0099 */
+	/* Has ID 0x0099 when not in "Advanced Driver" mode.
+	 * The UM-2EX has only one input, but we cannot detect this. */
 	USB_DEVICE(0x0582, 0x0005),
 	.driver_info = (unsigned long) & (const struct snd_usb_audio_quirk) {
 		.vendor_name = "EDIROL",
@@ -385,7 +386,7 @@ YAMAHA_DEVICE(0x7010, "UB99"),
 	}
 },
 {
-	/* a later revision uses ID 0x009d */
+	/* has ID 0x009d when not in "Advanced Driver" mode */
 	USB_DEVICE(0x0582, 0x0009),
 	.driver_info = (unsigned long) & (const struct snd_usb_audio_quirk) {
 		.vendor_name = "EDIROL",