ASoC: fsl_micfil: Enable default case in micfil_set_quality()

If 'micfil->quality' received from micfil_quality_set() somehow ends
up with an unpredictable value, switch() operator will fail to
initialize local variable qsel before regmap_update_bits() tries
to utilize it.

While it is unlikely, play it safe and enable a default case that
returns -EINVAL error.

Found by Linux Verification Center (linuxtesting.org) with static
analysis tool SVACE.

Fixes: bea1d61d5892 ("ASoC: fsl_micfil: rework quality setting")
Cc: [e-mail]
Signed-off-by: Nikita Zhandarovich <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

sound/soc/fsl/fsl_micfil.c

···
 	case QUALITY_VLOW2:
 		qsel = MICFIL_QSEL_VLOW2_QUALITY;
 		break;
+	default:
+		return -EINVAL;
 	}
 
 	return regmap_update_bits(micfil->regmap, REG_MICFIL_CTRL2,