add ocean depth fix for cnrm_esm2_1 (#1069)

esmvalcore/cmor/_fixes/cmip6/cnrm_esm2_1.py

@@ -1,9 +1,40 @@
 """Fixes for CNRM-ESM2-1 model."""
+from iris.cube import CubeList
+
 from .cnrm_cm6_1 import Cl as BaseCl
 from .cnrm_cm6_1 import Clcalipso as BaseClcalipso
 from .cnrm_cm6_1 import Cli as BaseCli
 from .cnrm_cm6_1 import Clw as BaseClw
 
+from ..fix import Fix
+from ..shared import (set_ocean_depth_coord)
+
+
+class Omon(Fix):
+    """Fixes for ocean variables."""
+
+    def fix_metadata(self, cubes):
+        """
+        Fix ocean depth coordinate.
+
+        Parameters
+        ----------
+        cubes: iris CubeList
+            List of cubes to fix
+
+        Returns
+        -------
+        iris.cube.CubeList
+
+        """
+        new_list = CubeList()
+        for cube in cubes:
+            if cube.coords(axis='Z'):
+                if not cube.coord(axis='Z').standard_name:
+                    cube = set_ocean_depth_coord(cube)
+            new_list.append(cube)
+        return CubeList(new_list)
+
 
 Cl = BaseCl