Fingerprint: add new signature method

commit c42a54795d introcuded a bug by
using fp.to_string(). Replace this with fp.signature() which correctly
returns the full fingerprint instead of the short version.

Signed-off-by: Dietmar Maurer <dietmar@proxmox.com>

src/api2/tape/drive.rs

@@ -696,7 +696,7 @@ pub async fn read_label(
                         flat.encryption_key_fingerprint = set
                             .encryption_key_fingerprint
                             .as_ref()
-                            .map(|fp| fp.to_string());
+                            .map(|fp| fp.signature());
 
                         let encrypt_fingerprint = set.encryption_key_fingerprint.clone()
                             .map(|fp| (fp, set.uuid.clone()));