ALSA: au88xx: Add fall-through annotations

As a preparatory patch for the upcoming -Wimplicit-fallthrough
compiler checks, add the "fall through" annotation in au88xx driver.

Although the usages in both both functions vortex_adbdma_setbuffers()
and vortex_wtdma_setbuffers() look a bit suspicious, we keep the
behavior as before, just to be safer.  If it were broken, we should
have already received bug reports.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/au88x0/au88x0_core.c

@@ -1115,6 +1115,7 @@ vortex_adbdma_setbuffers(vortex_t * vortex, int adbdma,
 		hwwrite(vortex->mmio,
 			VORTEX_ADBDMA_BUFBASE + (adbdma << 4) + 0xc,
 			snd_pcm_sgbuf_get_addr(dma->substream, psize * 3));
+		/* fall through */
 		/* 3 pages */
 	case 3:
 		dma->cfg0 |= 0x12000000;
@@ -1122,12 +1123,14 @@ vortex_adbdma_setbuffers(vortex_t * vortex, int adbdma,
 		hwwrite(vortex->mmio,
 			VORTEX_ADBDMA_BUFBASE + (adbdma << 4) + 0x8,
 			snd_pcm_sgbuf_get_addr(dma->substream, psize * 2));
+		/* fall through */
 		/* 2 pages */
 	case 2:
 		dma->cfg0 |= 0x88000000 | 0x44000000 | 0x10000000 | (psize - 1);
 		hwwrite(vortex->mmio,
 			VORTEX_ADBDMA_BUFBASE + (adbdma << 4) + 0x4,
 			snd_pcm_sgbuf_get_addr(dma->substream, psize));
+		/* fall through */
 		/* 1 page */
 	case 1:
 		dma->cfg0 |= 0x80000000 | 0x40000000 | ((psize - 1) << 0xc);
@@ -1390,17 +1393,20 @@ vortex_wtdma_setbuffers(vortex_t * vortex, int wtdma,
 		dma->cfg1 |= 0x88000000 | 0x44000000 | 0x30000000 | (psize-1);
 		hwwrite(vortex->mmio, VORTEX_WTDMA_BUFBASE + (wtdma << 4) + 0xc,
 			snd_pcm_sgbuf_get_addr(dma->substream, psize * 3));
+		/* fall through */
 		/* 3 pages */
 	case 3:
 		dma->cfg0 |= 0x12000000;
 		dma->cfg1 |= 0x80000000 | 0x40000000 | ((psize-1) << 0xc);
 		hwwrite(vortex->mmio, VORTEX_WTDMA_BUFBASE + (wtdma << 4)  + 0x8,
 			snd_pcm_sgbuf_get_addr(dma->substream, psize * 2));
+		/* fall through */
 		/* 2 pages */
 	case 2:
 		dma->cfg0 |= 0x88000000 | 0x44000000 | 0x10000000 | (psize-1);
 		hwwrite(vortex->mmio, VORTEX_WTDMA_BUFBASE + (wtdma << 4) + 0x4,
 			snd_pcm_sgbuf_get_addr(dma->substream, psize));
+		/* fall through */
 		/* 1 page */
 	case 1:
 		dma->cfg0 |= 0x80000000 | 0x40000000 | ((psize-1) << 0xc);