staging: greybus: Add remaining audio files to maintained list

Some Greybus Audio Device Class Protocol driver files are missing
in the MAINTAINERS file even though they are maintained so add
them.

CC: Vaibhav Agarwal <vaibhav.sr@gmail.com>
Signed-off-by: Mark Greer <mgreer@animalcreek.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

MAINTAINERS

@@ -5301,7 +5301,16 @@ GREYBUS AUDIO PROTOCOLS DRIVERS
 M:	Vaibhav Agarwal <vaibhav.sr@gmail.com>
 M:	Mark Greer <mgreer@animalcreek.com>
 S:	Maintained
+F:	drivers/staging/greybus/audio_apbridgea.c
+F:	drivers/staging/greybus/audio_apbridgea.h
 F:	drivers/staging/greybus/audio_codec.c
+F:	drivers/staging/greybus/audio_codec.h
+F:	drivers/staging/greybus/audio_gb.c
+F:	drivers/staging/greybus/audio_manager.c
+F:	drivers/staging/greybus/audio_manager.h
+F:	drivers/staging/greybus/audio_manager_module.c
+F:	drivers/staging/greybus/audio_manager_private.h
+F:	drivers/staging/greybus/audio_manager_sysfs.c
 F:	drivers/staging/greybus/audio_module.c
 F:	drivers/staging/greybus/audio_topology.c