As the name indicates, PERST# is active low. Fix the DT description to
match the HW behaviour.

Fixes: ff2a8d91 ("arm64: apple: Add PCIe node")
Link: https://lore.kernel.org/r/20211123180636.80558-3-maz@kernel.orgSigned-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Luca Ceresoli <luca@lucaceresoli.net>
Reviewed-by: Mark Kettenis <kettenis@openbsd.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>