ALSA: scarlett2: Rename db_scale_scarlett2_gain to volume

db_scale_scarlett2_gain is the TLV for the output volume controls.
Gen 4 has software-controllable input gain controls, so rename this to
db_scale_scarlett2_volume so we can use that name for the inputs.
Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/d544ec7cc5d5a849da104a5a78b17f61f50657c1.1703444932.git.g@b4.vuSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_scarlett2.c

@@ -2417,7 +2417,7 @@ static int scarlett2_volume_ctl_put(struct snd_kcontrol *kctl,
 }
 
 static const DECLARE_TLV_DB_MINMAX(
-	db_scale_scarlett2_gain, -SCARLETT2_VOLUME_BIAS * 100, 0
+	db_scale_scarlett2_volume, -SCARLETT2_VOLUME_BIAS * 100, 0
 );
 
 static const struct snd_kcontrol_new scarlett2_master_volume_ctl = {
@@ -2428,7 +2428,7 @@ static const struct snd_kcontrol_new scarlett2_master_volume_ctl = {
 	.info = scarlett2_volume_ctl_info,
 	.get  = scarlett2_master_volume_ctl_get,
 	.private_value = 0, /* max value */
-	.tlv = { .p = db_scale_scarlett2_gain }
+	.tlv = { .p = db_scale_scarlett2_volume }
 };
 
 static const struct snd_kcontrol_new scarlett2_line_out_volume_ctl = {
@@ -2440,7 +2440,7 @@ static const struct snd_kcontrol_new scarlett2_line_out_volume_ctl = {
 	.get  = scarlett2_volume_ctl_get,
 	.put  = scarlett2_volume_ctl_put,
 	.private_value = 0, /* max value */
-	.tlv = { .p = db_scale_scarlett2_gain }
+	.tlv = { .p = db_scale_scarlett2_volume }
 };
 
 /*** Mute Switch Controls ***/