PCI: keystone: Don't discard .probe() callback

The __init annotation makes the ks_pcie_probe() function disappear after
booting completes. However a device can also be bound later. In that case,
we try to call ks_pcie_probe(), but the backing memory is likely already
overwritten.

The right thing to do is do always have the probe callback available.  Note
that the (wrong) __refdata annotation prevented this issue to be noticed by
modpost.

Fixes: 0c4ffcfe

 ("PCI: keystone: Add TI Keystone PCIe driver")
Link: https://lore.kernel.org/r/20231001170254.2506508-5-u.kleine-koenig@pengutronix.de
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org