maint: fix "mixing declarations and code" errors

maint: fix "mixing declarations and code" errors

clang 14.0.5 complains:

../src/bhyve/bhyve_device.c:42:29: error: mixing declarations and code
is incompatible with standards before C99
[-Werror,-Wdeclaration-after-statement]
    virDomainPCIAddressSet *addrs = opaque;
                            ^
1 error generated.

And a few similar errors in some other places, mainly bhyve related.
Apply a trivial fix to resolve that.

Signed-off-by: Roman Bogorodskiy <bogorodskiy@gmail.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>