pci: Don't register a specialized 'config_write' if default behavior is intended

pci: Don't register a specialized 'config_write' if default behavior is intended

Few devices have their specialized 'config_write' methods which simply
call 'pci_default_write_config' followed by a 'msix_write_config' or
'msi_write_config' calls, using exact same arguments.

This is unnecessary as 'pci_default_write_config' already invokes
'msi_write_config' and 'msix_write_config'.

Also, since 'pci_default_write_config' is the default 'config_write'
handler, we can simply avoid the registration of these specialized
versions.

Cc: Leonid Shatz <leonid.shatz@ravellosystems.com>
Signed-off-by: Shmulik Ladkani <shmulik.ladkani@ravellosystems.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>