[POWERPC] CPM_UART: Fix inconsistency of function definition

The below hunk was missed from the recent patch, and now, there are somewhat
inconsistent definitions:

in cpm_uart.h:
int __init cpm_uart_init_portdesc(void);

in cpm_uart_cpm1.c:
int __init cpm_uart_init_portdesc(void)
{
}

in cpm_uart_cpm2.c:
int cpm_uart_init_portdesc(void)
{
}

Signed-off-by: Kalle Pokki <kalle.pokki@iki.fi>
Signed-off-by: Vitaly Bordug <vbordug@ru.mvista.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>