powerpc/perf: Fix misleading comment in pmao_restore_workaround()

The current comment in pmao_restore_workaround() regarding
hard_irq_disable() is wrong. It should say to hard *disable* interrupts
instead of *enable*. Fix it.

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