virhostdev: Unify virDomainHostdevDef to virPCIDevice translation

virhostdev: Unify virDomainHostdevDef to virPCIDevice translation

There are two places where we need to create virPCIDevice from
given virDomainHostdevDef. In both places the code is duplicated.
Move them into a single function and call it from those two
places.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Tested-by: Daniel Henrique Barboza <danielhb413@gmail.com>