qemu: Use the proper string in qemuBlock...JSONSocketAddress()

Recent refactors made it so that the function may use uninitialized
pointer, but it actually wanted to use a different variable and value
at all.
Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>

src/qemu/qemu_block.c

@@ -482,7 +482,7 @@ qemuBlockStorageSourceBuildHostsJSONSocketAddress(virStorageSourcePtr src,
         case VIR_STORAGE_NET_HOST_TRANS_LAST:
             virReportError(VIR_ERR_INTERNAL_ERROR,
                            _("transport protocol '%s' is not yet supported"),
-                           transport);
+                           virStorageNetHostTransportTypeToString(host->transport));
             goto cleanup;
         }