PCI: apple: Fix PERST# polarity

PCI: apple: Fix PERST# polarity

Now that PERST# is properly defined as active-low in the device tree, fix
the driver to correctly drive the line independently of the implied
polarity.

Suggested-by: Pali Rohár <pali@kernel.org>
Fixes: c20870b4ee0c ("PCI: apple: Add initial hardware bring-up")
Link: https://lore.kernel.org/r/20211123180636.80558-4-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Luca Ceresoli <luca@lucaceresoli.net>