qemu: blockcopy: Use the mirror disk source to label the files

Use the source struct and the corresponding function so that we can
avoid using the path separately. Now that
qemuDomainPrepareDiskChainElementPath isn't use anywhere, we can safely
remove it.

Additionally, the removal fixes a misaligned comment as the removed
function was added under a comment for a different function.

src/qemu/qemu_driver.c

@@ -12129,25 +12129,6 @@ qemuDomainPrepareDiskChainElement(virQEMUDriverPtr driver,
 /* Return -1 if request is not sent to agent due to misconfig, -2 if request
  * is sent but failed, and number of frozen filesystems on success. If -2 is
  * returned, FSThaw should be called revert the quiesced status. */
-static int
-qemuDomainPrepareDiskChainElementPath(virQEMUDriverPtr driver,
-                                      virDomainObjPtr vm,
-                                      virDomainDiskDefPtr disk,
-                                      const char *file,
-                                      qemuDomainDiskChainMode mode)
-{
-    virStorageSource src;
-
-    memset(&src, 0, sizeof(src));
-
-    src.type = VIR_STORAGE_TYPE_FILE;
-    src.format = VIR_STORAGE_FILE_RAW;
-    src.path = (char *) file; /* casting away const is safe here */
-
-    return qemuDomainPrepareDiskChainElement(driver, vm, disk, &src, mode);
-}
-
-
 static int
 qemuDomainSnapshotFSFreeze(virQEMUDriverPtr driver,
                            virDomainObjPtr vm,
@@ -15429,10 +15410,10 @@ qemuDomainBlockCopy(virDomainObjPtr vm,
     if (VIR_STRDUP(mirror->path, dest) < 0)
         goto endjob;
 
-    if (qemuDomainPrepareDiskChainElementPath(driver, vm, disk, dest,
-                                              VIR_DISK_CHAIN_READ_WRITE) < 0) {
-        qemuDomainPrepareDiskChainElementPath(driver, vm, disk, dest,
-                                              VIR_DISK_CHAIN_NO_ACCESS);
+    if (qemuDomainPrepareDiskChainElement(driver, vm, disk, mirror,
+                                          VIR_DISK_CHAIN_READ_WRITE) < 0) {
+        qemuDomainPrepareDiskChainElement(driver, vm, disk, mirror,
+                                          VIR_DISK_CHAIN_NO_ACCESS);
         goto endjob;
     }
 
@@ -15443,8 +15424,8 @@ qemuDomainBlockCopy(virDomainObjPtr vm,
     virDomainAuditDisk(vm, NULL, mirror, "mirror", ret >= 0);
     qemuDomainObjExitMonitor(driver, vm);
     if (ret < 0) {
-        qemuDomainPrepareDiskChainElementPath(driver, vm, disk, dest,
-                                              VIR_DISK_CHAIN_NO_ACCESS);
+        qemuDomainPrepareDiskChainElement(driver, vm, disk, mirror,
+                                          VIR_DISK_CHAIN_NO_ACCESS);
         goto endjob;
     }