powerpc: annotate implicit fall throughs

There is a plan to build the kernel with -Wimplicit-fallthrough and these
places in the code produced warnings, but because we build arch/powerpc
with -Werror, they became errors.  Fix them up.

This patch produces no change in behaviour, but should be reviewed in
case these are actually bugs not intentional fallthoughs.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/nvram_64.c

@@ -809,6 +809,7 @@ static long dev_nvram_ioctl(struct file *file, unsigned int cmd,
 #ifdef CONFIG_PPC_PMAC
 	case OBSOLETE_PMAC_NVRAM_GET_OFFSET:
 		printk(KERN_WARNING "nvram: Using obsolete PMAC_NVRAM_GET_OFFSET ioctl\n");
+		/* fall through */
 	case IOC_NVRAM_GET_OFFSET: {
 		int part, offset;