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

commit 200bddbb upstream.

With CONFIG_PCIE_KEYSTONE=y and ks_pcie_remove() marked with __exit, the
function is discarded from the driver. In this case a bound device can
still get unbound, e.g via sysfs. Then no cleanup code is run resulting in
resource leaks or worse.

The right thing to do is do always have the remove callback available.
Note that this driver cannot be compiled as a module, so ks_pcie_remove()
was always discarded before this change and modpost couldn't warn about
this issue. Furthermore the __ref annotation also prevents a warning.

Fixes: 0c4ffcfe

 ("PCI: keystone: Add TI Keystone PCIe driver")
Link: https://lore.kernel.org/r/20231001170254.2506508-4-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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>