powerpc/kdump64: Don't reference freed memory as pacas

powerpc/kdump64: Don't reference freed memory as pacas

Starting with 0ba00dd5f05fef8b3b1ef2de853fcc708ebb140f (powerpc:
Dynamically allocate pacas) the space for pacas beyond cpu_possible
is freed, but we failed to update the loop in crash.c.

Since 7896e4f4dd4ce85e11edf1dc3946d86ce0a84d6e (powerpc: Set nr_cpu_ids
early and use it to free PACAs) the number of pacas allocated is
always nr_cpu_ids.

Signed-off-by: Milton Miller <miltonm@bga.com>
Cc: <stable@kernel.org> # .34.x
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>