fixup! ACPI / PPTT: Provide a helper to walk processor containers

Fix off-by-one error validating the bounds of processor nodes at the
end of the PPTT.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>

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This issue resulted from copy-pasting other broken code in the PPTT
parser, since fixed upstream in:

ACPI: PPTT: Fix processor subtable walk

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/acpi/pptt.c?id=adfab6b39202481bb43286fff94def4953793fdb