ALSA: usb-audio: Fix an out-of-bound read in create_composite_quirks

In `create_composite_quirk`, the terminating condition of for loops is
`quirk->ifnum < 0`. So any composite quirks should end with `struct
snd_usb_audio_quirk` object with ifnum < 0.

    for (quirk = quirk_comp->data; quirk->ifnum >= 0; ++quirk) {

    	.....
    }

the data field of Bower's & Wilkins PX headphones usb device device quirks
do not end with {.ifnum = -1}, wihch may result in out-of-bound read.

This Patch fix the bug by adding an ending quirk object.

Fixes: 240a8af929 ("ALSA: usb-audio: Add a quirck for B&W PX headphones")
Signed-off-by: Hui Peng <benquike@163.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/quirks-table.h

@@ -3326,6 +3326,9 @@ AU0828_DEVICE(0x2040, 0x7270, "Hauppauge", "HVR-950Q"),
 					}
 				}
 			},
+			{
+				.ifnum = -1
+			},
 		}
 	}
 },
@@ -3369,6 +3372,9 @@ AU0828_DEVICE(0x2040, 0x7270, "Hauppauge", "HVR-950Q"),
 					}
 				}
 			},
+			{
+				.ifnum = -1
+			},
 		}
 	}
 },