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