ALSA: opti92x: mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Addresses-Coverity-ID: 1165394 ("Missing break in switch")
Addresses-Coverity-ID: 1167851 ("Missing break in switch")
Addresses-Coverity-ID: 402015 ("Missing break in switch")
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Takashi Iwai <[e-mail]>

sound/isa/opti9xx/opti92x-ad1848.c

···
 			retval = inb(chip->mc_base + 9);
 			break;
 		}
+		/* Fall through */
 
 	case OPTi9XX_HW_82C928:
 	case OPTi9XX_HW_82C929:
···
 			outb(value, chip->mc_base + 9);
 			break;
 		}
+		/* Fall through */
 
 	case OPTi9XX_HW_82C928:
 	case OPTi9XX_HW_82C929:
···
 		snd_opti9xx_write_mask(chip, OPTi9XX_MC_REG(4), 0xf0, 0xfc);
 		/* enable wave audio */
 		snd_opti9xx_write_mask(chip, OPTi9XX_MC_REG(6), 0x02, 0x02);
+		/* Fall through */
 
 	case OPTi9XX_HW_82C925:
 		/* enable WSS mode */