staging: mt7621-pci: use pcie_[read|write] in [write|read]_config

Instead of custom macros use pcie_read and pcie_write functions.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Tested-by: NeilBrown <neil@brown.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>