powerpc/32s: fix initial setup of segment registers on secondary CPU

The patch referenced below moved the loading of segment registers
out of load_up_mmu() in order to do it earlier in the boot sequence.
However, the secondary CPU still needs it to be done when loading up
the MMU.

Reported-by: Erhard F. <erhard_f@mailbox.org>
Fixes: 215b8237 ("powerpc/32s: set up an early static hash table for KASAN")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>