ALSA: scarlett2: Fix Scarlett 4th Gen input gain range

The input gain range TLV was declared as -70dB to 0dB, but the preamp
gain range is actually 0dB to +70dB. Rename SCARLETT2_GAIN_BIAS to
SCARLETT2_MAX_GAIN and update the TLV to fix.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Fixes: 0a995e3 ("ALSA: scarlett2: Add support for software-controllable input gain")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Message-ID: <9168317b5ac5335943d3f14dbcd1cc2d9b2299d0.1710047969.git.g@b4.vu>

Author: geoffreybennett

sound/usb/mixer_scarlett2.c

@@ -173,7 +173,9 @@
 
 /* some gui mixers can't handle negative ctl values */
 #define SCARLETT2_VOLUME_BIAS 127
-#define SCARLETT2_GAIN_BIAS 70
+
+/* maximum preamp input gain */
+#define SCARLETT2_MAX_GAIN 70
 
 /* mixer range from -80dB to +6dB in 0.5dB steps */
 #define SCARLETT2_MIXER_MIN_DB -80
@@ -3464,7 +3466,7 @@ static int scarlett2_input_gain_ctl_info(struct snd_kcontrol *kctl,
 	uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
 	uinfo->count = elem->channels;
 	uinfo->value.integer.min = 0;
-	uinfo->value.integer.max = SCARLETT2_GAIN_BIAS;
+	uinfo->value.integer.max = SCARLETT2_MAX_GAIN;
 	uinfo->value.integer.step = 1;
 
 unlock:
@@ -3541,7 +3543,7 @@ static int scarlett2_input_gain_ctl_put(struct snd_kcontrol *kctl,
 }
 
 static const DECLARE_TLV_DB_MINMAX(
-	db_scale_scarlett2_gain, -SCARLETT2_GAIN_BIAS * 100, 0
+	db_scale_scarlett2_gain, 0, SCARLETT2_MAX_GAIN * 100
 );
 
 static const struct snd_kcontrol_new scarlett2_input_gain_ctl = {