pci: avoid losing config updates to MSI/MSIX cap regs

pci: avoid losing config updates to MSI/MSIX cap regs

Since
commit 95d658002401e2e47a5404298ebe9508846e8a39
    msi: Invoke msi/msix_write_config from PCI core
msix config writes are lost, the value written is always 0.

Fix pci_default_write_config to avoid this.

Cc: qemu-stable@nongnu.org
Signed-off-by: Knut Omang <knut.omang@oracle.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit d7efb7e08e5edaac23b0dc824f72c3f353447c39)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>