powerpc/xmon: Fix compile error in print_insn* functions

Fix couple of compile errors I stumbled upon with CONFIG_XMON=y and
CONFIG_XMON_DISASSEMBLY=n

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200123010455.GA15080@us.ibm.com