[ALSA] usb-audio - allow USB MIDI quirks to specify endpoints explicitly

USB generic driver
This patch reintroduces the check for endpoint numbers that are
specified explicitly in the quirk structure.
This check was accidentally dropped in the last rewrite of
snd_usbmidi_detect_endpoints().
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

sound/usb/usbmidi.c

@@ -1229,6 +1229,9 @@ static int snd_usbmidi_detect_endpoints(snd_usb_midi_t* umidi,
 	if (le16_to_cpu(umidi->chip->dev->descriptor.idVendor) == 0x0582)
 		snd_usbmidi_switch_roland_altsetting(umidi);
 
+	if (endpoint[0].out_ep || endpoint[0].in_ep)
+		return 0;	
+
 	intf = umidi->iface;
 	if (!intf || intf->num_altsetting < 1)
 		return -ENOENT;