powerpc/CPM: Minor cosmetic changes to udbg_putc

udbg_putc is a *function pointer* that is initialized during
udbg_init_cpm. It might not be initialized properly when called from
udbg_putc_cpm(), so (recursively) call udbg_putc_cpm() directly.

Signed-off-by: Nye Liu <nyet@mrv.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>