ALSA: mixart: hard dependency on the standard fw loader

It makes no longer sense to keep the old hwdep user-space firmware
loading, which has been deprecated since ages ago.

Just add a hard dependency on CONFIG_FW_LOADER and drop the useless
code.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/pci/Kconfig b/sound/pci/Kconfig
index 6150eb1..4356892 100644
--- a/sound/pci/Kconfig
+++ b/sound/pci/Kconfig
@@ -707,6 +707,7 @@
 
 config SND_MIXART
 	tristate "Digigram miXart"
+	select FW_LOADER
 	select SND_HWDEP
 	select SND_PCM
 	help