conf: drop redundant parameters during probe

conf: drop redundant parameters during probe

Now that each virStorageSource can track allocation information,
and given that we already have the information without extra
syscalls, it's easier to just always populate the information
directly into the struct than it is to sometimes pass the address
of the struct members down the call chain.

* src/storage/storage_backend.h (virStorageBackendUpdateVolInfo)
(virStorageBackendUpdateVolTargetInfo)
(virStorageBackendUpdateVolTargetInfoFD): Update signature.
* src/storage/storage_backend.c (virStorageBackendUpdateVolInfo)
(virStorageBackendUpdateVolTargetInfo)
(virStorageBackendUpdateVolTargetInfoFD): Always populate struct
members instead.
* src/storage/storage_backend_disk.c
(virStorageBackendDiskMakeDataVol): Update client.
* src/storage/storage_backend_fs.c (virStorageBackendProbeTarget)
(virStorageBackendFileSystemRefresh)
(virStorageBackendFileSystemVolRefresh): Likewise.
* src/storage/storage_backend_gluster.c
(virStorageBackendGlusterRefreshVol): Likewise.
* src/storage/storage_backend_logical.c
(virStorageBackendLogicalMakeVol): Likewise.
* src/storage/storage_backend_mpath.c
(virStorageBackendMpathNewVol): Likewise.
* src/storage/storage_backend_scsi.c
(virStorageBackendSCSINewLun): Likewise.

Signed-off-by: Eric Blake <eblake@redhat.com>