powerpc/powermac: Fix build error seen with powermac smp builds

powermac smp builds fail with

arch/powerpc/platforms/powermac/smp.c: In function 'smp_psurge_probe':
arch/powerpc/platforms/powermac/smp.c:278:3: error:
		'return' with a value, in function returning void

There are several instances of this error.

Fixes: a7f4ee1f ("powerpc: Drop return value of smp_ops->probe()")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>