PCI: hisi: Fix hisi_pcie_cfg_read() 32-bit reads

For 32-bit config reads (size == 4), hisi_pcie_cfg_read() returned success
but never filled in the data we read.

Return the register data for 32-bit config reads.

Without this fix, PCI doesn't work at all because enumeration depends on
32-bit config reads.  The driver was tested internally, but got broken in
the process of upstreaming, so this fixes the breakage.

Fixes: 500a1d9a ("PCI: hisi: Add HiSilicon SoC Hip05 PCIe driver")
Signed-off-by: Dongdong Liu <liudongdong3@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Zhou Wang <wangzhou1@hisilicon.com>