pci: xilinx: Fix "reg" not found error

Fix the driver to use the dev_read_addr_size API to fetch the reg
property from the DT.

Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Link: https://lore.kernel.org/r/20231116165103.140968-2-mchitale@ventanamicro.com


Signed-off-by: Michal Simek <michal.simek@amd.com>