MAINTAINERS: update entry for firewire audio drivers with UAPI header

The most of drivers in ALSA firewire stack supports common ioctl commands
to enable/disable packet streaming as well as some ioctl commands for
model-specific features. An UAPI header is exported to userspace.

This commit adds supplement for entry of ALSA firewire stack with a path
of the UAPI header.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

MAINTAINERS

@@ -6271,6 +6271,7 @@ L:	alsa-devel@alsa-project.org (moderated for non-subscribers)
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git
 S:	Maintained
 F:	sound/firewire/
+F:	include/uapi/sound/firewire.h
 
 FIREWIRE MEDIA DRIVERS (firedtv)
 M:	Stefan Richter <stefanr@s5r6.in-berlin.de>