BOOT: Show that no_ipi_broadcast() takes a parameter.

a rather obvious fix given the opening of the function:

...
static __init int no_ipi_broadcast(char *str)
{
        get_option(&str, &no_broadcast);
...

Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Signed-off-by: Adrian Bunk <bunk@kernel.org>