ALSA: usb-audio: scarlett2: Add sw_hw_ctls and mux_ctls

Save the struct snd_kcontrol pointers for the sw_hw and mux controls.
This is in preparation for speaker switching support which needs to be
able to update those controls.
Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/269d89181bf29dbea80ba6f8cfff84fb23b77f86.1624379707.git.g@b4.vuSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_scarlett_gen2.c

@@ -394,12 +394,14 @@ struct scarlett2_data {
 	struct snd_kcontrol *sync_ctl;
 	struct snd_kcontrol *master_vol_ctl;
 	struct snd_kcontrol *vol_ctls[SCARLETT2_ANALOGUE_MAX];
+	struct snd_kcontrol *sw_hw_ctls[SCARLETT2_ANALOGUE_MAX];
 	struct snd_kcontrol *mute_ctls[SCARLETT2_ANALOGUE_MAX];
 	struct snd_kcontrol *dim_mute_ctls[SCARLETT2_DIM_MUTE_COUNT];
 	struct snd_kcontrol *level_ctls[SCARLETT2_LEVEL_SWITCH_MAX];
 	struct snd_kcontrol *pad_ctls[SCARLETT2_PAD_SWITCH_MAX];
 	struct snd_kcontrol *air_ctls[SCARLETT2_AIR_SWITCH_MAX];
 	struct snd_kcontrol *phantom_ctls[SCARLETT2_PHANTOM_SWITCH_MAX];
+	struct snd_kcontrol *mux_ctls[SCARLETT2_MUX_MAX];
 	struct snd_kcontrol *direct_monitor_ctl;
 	u8 mux[SCARLETT2_MUX_MAX];
 	u8 mix[SCARLETT2_INPUT_MIX_MAX * SCARLETT2_OUTPUT_MIX_MAX];
@@ -2558,7 +2560,8 @@ static int scarlett2_add_line_out_ctls(struct usb_mixer_interface *mixer)
 				 i + 1);
 			err = scarlett2_add_new_ctl(mixer,
 						    &scarlett2_sw_hw_enum_ctl,
-						    i, 1, s, NULL);
+						    i, 1, s,
+						    &private->sw_hw_ctls[i]);
 			if (err < 0)
 				return err;
 		}
@@ -2876,7 +2879,8 @@ static int scarlett2_add_mux_enums(struct usb_mixer_interface *mixer)
 
 			err = scarlett2_add_new_ctl(mixer,
 						    &scarlett2_mux_src_enum_ctl,
-						    i, 1, s, NULL);
+						    i, 1, s,
+						    &private->mux_ctls[i]);
 			if (err < 0)
 				return err;
 		}