ALSA: oxfw: fix detect_loud_models() return value

This code causes a static checker warning:

	sound/firewire/oxfw/oxfw.c:46 detect_loud_models()
	warn: signedness bug returning '(-2)'

The detect_loud_models() function should return false on falure, so that
we don't try to set up the loud code for hardware that doesn't support
it.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/firewire/oxfw/oxfw.c

@@ -43,7 +43,7 @@ static bool detect_loud_models(struct fw_unit *unit)
 	err = fw_csr_string(unit->directory, CSR_MODEL,
 			    model, sizeof(model));
 	if (err < 0)
-		return err;
+		return false;
 
 	for (i = 0; i < ARRAY_SIZE(models); i++) {
 		if (strcmp(models[i], model) == 0)