MAINTAINERS: Correct Cadence PCI driver path

MAINTAINERS: Correct Cadence PCI driver path

54d70f0492d2 ("PCI: cadence: Move all files to per-device cadence
directory") moved files of the PCI cadence drivers, but did not update the
MAINTAINERS entry.

Since then, ./scripts/get_maintainer.pl --self-test complains:

  warning: no file matches F: drivers/pci/controller/pcie-cadence*

Repair the MAINTAINERS entry.

Link: https://lore.kernel.org/r/20200221185402.4703-1-lukas.bulwahn@gmail.com
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>