block: do not check bdrv_file_open

The set of BlockDrivers that have .bdrv_file_open coincides with those
that have .protocol_name and guess what---checking drv->bdrv_file_open
is done to see if the driver is a protocol.  So check drv->protocol_name
instead.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
1 file changed