powerpc: Fix misleading comment in early_setup_secondary()

Current comment in the early_setup_secondary() for paca->soft_enabled
update is misleading. Comment should say to Mark interrupts "disabled"
instead of "enabled". Fix the typo.

Signed-off-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>