util: Resolve Coverity FORWARD_NULL
util: Resolve Coverity FORWARD_NULL

Convert virPCIDriverFile to return the buffer allocated (or not) and make the
appropriate check in the caller.

Signed-off-by: John Ferlan <87558058f6f829e5ec976c8ef960720af4ff9c7d@redhat.com>

taget/libvirt,datto/libvirt,jardasgit/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,eskultety/libvirt,nertpinx/libvirt,agx/libvirt,fabianfreyer/libvirt,rlaager/libvirt,nertpinx/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,zippy2/libvirt,libvirt/libvirt,nertpinx/libvirt,zippy2/libvirt,olafhering/libvirt,VenkatDatta/libvirt,rlaager/libvirt,fabianfreyer/libvirt,zippy2/libvirt,jfehlig/libvirt,rlaager/libvirt,jardasgit/libvirt,libvirt/libvirt,olafhering/libvirt,agx/libvirt,taget/libvirt,VenkatDatta/libvirt,datto/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,agx/libvirt,crobinso/libvirt,VenkatDatta/libvirt,jfehlig/libvirt,libvirt/libvirt,jardasgit/libvirt,eskultety/libvirt,crobinso/libvirt,datto/libvirt,taget/libvirt,eskultety/libvirt,olafhering/libvirt,libvirt/libvirt,rlaager/libvirt,jfehlig/libvirt,eskultety/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,agx/libvirt,crobinso/libvirt,datto/libvirt,nertpinx/libvirt,taget/libvirt,nertpinx/libvirt,datto/libvirt,andreabolognani/libvirt,eskultety/libvirt,rlaager/libvirt,olafhering/libvirt,jardasgit/libvirt,zippy2/libvirt,crobinso/libvirt,agx/libvirt,taget/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt