ALSA: opti92xx-ad1848: Use the standard fall-through annotation

As a preparatory patch for the upcoming -Wimplicit-fallthrough
compiler checks, replace with the standard "fall through" annotation
at the right places.  They have to be put right before the next
labels.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/isa/opti9xx/opti92x-ad1848.c

@@ -389,7 +389,8 @@ static int snd_opti9xx_configure(struct snd_opti9xx *chip,
 	case OPTi9XX_HW_82C931:
 		/* disable 3D sound (set GPIO1 as output, low) */
 		snd_opti9xx_write_mask(chip, OPTi9XX_MC_REG(20), 0x04, 0x0c);
-	case OPTi9XX_HW_82C933: /* FALL THROUGH */
+		/* fall through */
+	case OPTi9XX_HW_82C933:
 		/*
 		 * The BTC 1817DW has QS1000 wavetable which is connected
 		 * to the serial digital input of the OPTI931.
@@ -400,7 +401,8 @@ static int snd_opti9xx_configure(struct snd_opti9xx *chip,
 		 * or digital input signal.
 		 */
 		snd_opti9xx_write_mask(chip, OPTi9XX_MC_REG(26), 0x01, 0x01);
-	case OPTi9XX_HW_82C930: /* FALL THROUGH */
+		/* fall through */
+	case OPTi9XX_HW_82C930:
 		snd_opti9xx_write_mask(chip, OPTi9XX_MC_REG(6), 0x02, 0x03);
 		snd_opti9xx_write_mask(chip, OPTi9XX_MC_REG(3), 0x00, 0xff);
 		snd_opti9xx_write_mask(chip, OPTi9XX_MC_REG(4), 0x10 |