ALSA: usbmixer: rename usbmixer.[ch] -> mixer.[ch]

For clearer namespace, also rename usbmixer_maps.c -> mixer_maps.c

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Cc: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/mixer_quirks.c b/sound/usb/mixer_quirks.c
index d2f4dcd..56b6659 100644
--- a/sound/usb/mixer_quirks.c
+++ b/sound/usb/mixer_quirks.c
@@ -35,7 +35,7 @@
 #include <sound/info.h>
 
 #include "usbaudio.h"
-#include "usbmixer.h"
+#include "mixer.h"
 #include "mixer_quirks.h"
 #include "helper.h"