powerpc/64s: Fix PACA_IRQ_HARD_DIS accounting in idle_power4()

When idle_power4() hard disables interrupts then finds a soft pending
interrupt, it returns with interrupts hard disabled but without
PACA_IRQ_HARD_DIS set. Commit 9b81c021 ("powerpc/64s: make
PACA_IRQ_HARD_DIS track MSR[EE] closely") added a warning for that
condition (since disabled).

Fix this by adding the PACA_IRQ_HARD_DIS for that case.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>