[ALSA] Enable the analog loopback of the Revolution 5.1

Enable the analog loopback of the Revolution 5.1 card.
This patch adds support for the PT2258 volume controller and modifies
the Revolution 5.1 driver to make use of this facility.  This allows
to control the analog loopback of the card.

Signed-off-by: Jochen Voss <voss@seehuhn.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>
diff --git a/sound/i2c/Makefile b/sound/i2c/Makefile
index 816a2e7..45902d4 100644
--- a/sound/i2c/Makefile
+++ b/sound/i2c/Makefile
@@ -16,3 +16,4 @@
 # Toplevel Module Dependency
 obj-$(CONFIG_SND_INTERWAVE_STB) += snd-tea6330t.o snd-i2c.o
 obj-$(CONFIG_SND_ICE1712) += snd-cs8427.o snd-i2c.o
+obj-$(CONFIG_SND_ICE1724) += snd-i2c.o