ALSA: hda: realtek: fix incorrect IS_REACHABLE() usage

The alternative path leads to a build error after a recent change:

sound/pci/hda/patch_realtek.c: In function 'alc233_fixup_lenovo_low_en_micmute_led':
include/linux/stddef.h:9:14: error: called object is not a function or function pointer
    9 | #define NULL ((void *)0)
      |              ^
sound/pci/hda/patch_realtek.c:5041:49: note: in expansion of macro 'NULL'
 5041 | #define alc233_fixup_lenovo_line2_mic_hotkey    NULL
      |                                                 ^~~~
sound/pci/hda/patch_realtek.c:5063:9: note: in expansion of macro 'alc233_fixup_lenovo_line2_mic_hotkey'
 5063 |         alc233_fixup_lenovo_line2_mic_hotkey(codec, fix, action);

Using IS_REACHABLE() is somewhat questionable here anyway since it
leads to the input code not working when the HDA driver is builtin
but input is in a loadable module. Replace this with a hard compile-time
dependency on CONFIG_INPUT. In practice this won't chance much
other than solve the compiler error because it is rare to require
sound output but no input support.

Fixes: f603b15 ("ALSA: hda/realtek - add supported Mic Mute LED for Lenovo platform")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patch.msgid.link/20250304142620.582191-1-arnd@kernel.org
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/hda/Kconfig

@@ -222,6 +222,7 @@ comment "Set to Y if you want auto-loading the side codec driver"
 
 config SND_HDA_CODEC_REALTEK
 	tristate "Build Realtek HD-audio codec support"
+	depends on INPUT
 	select SND_HDA_GENERIC
 	select SND_HDA_GENERIC_LEDS
 	select SND_HDA_SCODEC_COMPONENT

sound/pci/hda/patch_realtek.c

@@ -4927,7 +4927,6 @@ static void alc298_fixup_samsung_amp_v2_4_amps(struct hda_codec *codec,
 		alc298_samsung_v2_init_amps(codec, 4);
 }
 
-#if IS_REACHABLE(CONFIG_INPUT)
 static void gpio2_mic_hotkey_event(struct hda_codec *codec,
 				   struct hda_jack_callback *event)
 {
@@ -5036,10 +5035,6 @@ static void alc233_fixup_lenovo_line2_mic_hotkey(struct hda_codec *codec,
 		spec->kb_dev = NULL;
 	}
 }
-#else /* INPUT */
-#define alc280_fixup_hp_gpio2_mic_hotkey	NULL
-#define alc233_fixup_lenovo_line2_mic_hotkey	NULL
-#endif /* INPUT */
 
 static void alc269_fixup_hp_line1_mic1_led(struct hda_codec *codec,
 				const struct hda_fixup *fix, int action)