powerpc/85xx: Fix fall-through warning for Clang

Fix the following fallthrough warning:

arch/powerpc/platforms/85xx/mpc85xx_cds.c:161:3: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://github.com/KSPP/linux/issues/198
Link: https://lore.kernel.org/lkml/202209061224.KxORRGVg-lkp@intel.com/
Link: https://lore.kernel.org/r/Yxe8XTY5C9qJLd0Z@work

arch/powerpc/platforms/85xx/mpc85xx_cds.c

@@ -159,6 +159,7 @@ static void __init mpc85xx_cds_pci_irq_fixup(struct pci_dev *dev)
 			else
 				dev->irq = 10;
 			pci_write_config_byte(dev, PCI_INTERRUPT_LINE, dev->irq);
+			break;
 		default:
 			break;
 		}