qemuMigrationSrcNBDStorageCopy: Return error code on error

In case the 'nbdURI' schema is not known the code would report an error
but wouldn't return failure.

Fixes: 49186372db
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>
Tested-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_migration.c

@@ -1154,6 +1154,7 @@ qemuMigrationSrcNBDStorageCopy(virQEMUDriver *driver,
             virReportError(VIR_ERR_INVALID_ARG,
                            _("Unsupported scheme in disks URI: %s"),
                            uri->scheme);
+            return -1;
         }
     }