trivial: Actually return an errno if reading cpuinfo fails
trivial: Actually return an errno if reading cpuinfo fails

We're not actually setting errno in read_whole_file()...

rpm-software-management/libhif,Conan-Kudo/libhif,cgwalters/libhif,edynox/libdnf,rpm-software-management/libhif,Conan-Kudo/libhif,hughsie/libhif,rpm-software-management/libdnf,rpm-software-management/libdnf,cgwalters/libhif,rpm-software-management/libhif,Conan-Kudo/libhif,hughsie/libhif,rpm-software-management/libhif,hughsie/libhif,Conan-Kudo/libhif,edynox/libdnf,hughsie/libhif,edynox/libdnf,cgwalters/libhif,edynox/libdnf,cgwalters/libhif,rpm-software-management/libdnf,rpm-software-management/libdnf