ALSA: hda/ca0132 - Use NULL instead of 0

Use NULL for initializing the snd_kcontrol_new.tlv field, instead of
0, as warned by sparse:
  sound/pci/hda/patch_ca0132.c:5519:22: warning: Using plain integer as NULL pointer

Also, the driver does the same initialization twice, once for
knew.tlv.c and another for knew.tlv.p while both point to the same
address (these are union).  Drop the latter superfluous one.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/hda/patch_ca0132.c

@@ -5516,8 +5516,7 @@ static int ca0132_alt_add_effect_slider(struct hda_codec *codec, hda_nid_t nid,
 
 	sprintf(namestr, "FX: %s %s Volume", pfx, dirstr[dir]);
 
-	knew.tlv.c = 0;
-	knew.tlv.p = 0;
+	knew.tlv.c = NULL;
 
 	switch (nid) {
 	case XBASS_XOVER: