scsi: sun3_scsi: Mark expected switch fall-throughs

Mark switch cases where we are expecting to fall through.

This patch fixes the following warnings:

drivers/scsi/sun3_scsi.c: warning: this statement may fall through
[-Wimplicit-fallthrough=]:  => 399:9, 403:9

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/sun3_scsi.c

@@ -397,10 +397,12 @@ static int sun3scsi_dma_finish(int write_flag)
 		case CSR_LEFT_3:
 			*vaddr = (dregs->bpack_lo & 0xff00) >> 8;
 			vaddr--;
+			/* Fall through */
 
 		case CSR_LEFT_2:
 			*vaddr = (dregs->bpack_hi & 0x00ff);
 			vaddr--;
+			/* Fall through */
 
 		case CSR_LEFT_1:
 			*vaddr = (dregs->bpack_hi & 0xff00) >> 8;