ALSA: usb-audio: Fix NULL dereference in create_fixed_stream_quirk()

create_fixed_stream_quirk() may cause a NULL-pointer dereference by
accessing the non-existing endpoint when a USB device with a malformed
USB descriptor is used.

This patch avoids it simply by adding a sanity check of bNumEndpoints
before the accesses.

Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=971125
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
static bool is_marantz_denon_dac(unsigned int id)
{
	switch (id) {
	case USB_ID(0x154e, 0x1003): /* Denon DA-300USB */
	case USB_ID(0x154e, 0x3005): /* Marantz HD-DAC1 */
	case USB_ID(0x154e, 0x3006): /* Marantz SA-14S1 */
		return true;
	}
	return false;
}

static bool is_marantz_denon_dac(unsigned int id)
{
	switch (id) {
	case USB_ID(0x154e, 0x1003): /* Denon DA-300USB */
	case USB_ID(0x154e, 0x3005): /* Marantz HD-DAC1 */
	case USB_ID(0x154e, 0x3006): /* Marantz SA-14S1 */
		return true;
	}
	return false;
}
