storage_file: Compute QCOW2 cluster size as ULL
storage_file: Compute QCOW2 cluster size as ULL

While the QCOW2 cluster size is represented in only 4 bits in the QCOW2
header and thus 1 << cluster_size cannot overflow int,
qcow2GetClusterSize is supposed to return unsigned long long so we can
just compute the result as ULL rather than computing it as int and
promoting to unsigned long long.

Signed-off-by: Jiri Denemark <62bdf77dc47919a4d59a91822129d14633cfca81@redhat.com>
Reviewed-by: Pavel Hrdina <d4772d05997b8abf035041e3b4f4996380ea7e7a@redhat.com>

crobinso/libvirt,jfehlig/libvirt,jfehlig/libvirt,olafhering/libvirt,nertpinx/libvirt,zippy2/libvirt,libvirt/libvirt,crobinso/libvirt,nertpinx/libvirt,nertpinx/libvirt,libvirt/libvirt,jfehlig/libvirt,crobinso/libvirt,nertpinx/libvirt,libvirt/libvirt,zippy2/libvirt,zippy2/libvirt,olafhering/libvirt,crobinso/libvirt,zippy2/libvirt,nertpinx/libvirt,jfehlig/libvirt,olafhering/libvirt,olafhering/libvirt,libvirt/libvirt