Diffusivity: Revert int_tide_CS to pointer

The redefining of int_tide_CS control struct in set_diffusivity_init
caused errors in debug-mode for Intel compilers.  The issue appears to
be an internal function that expects a pointer rather than the type.

This patch reverts this back to a pointer.  We can revisit this if there
is a need to reduce reliance on pointers.

Author: marshallward

src/parameterizations/vertical/MOM_set_diffusivity.F90

@@ -2201,7 +2201,7 @@ subroutine set_diffusivity_init(Time, G, GV, US, param_file, diag, CS, int_tide_
   type(diag_ctrl), target,  intent(inout) :: diag !< A structure used to regulate diagnostic output.
   type(set_diffusivity_CS), pointer       :: CS   !< pointer set to point to the module control
                                                   !! structure.
-  type(int_tide_CS),        intent(in), target :: int_tide_CSp !< Internal tide control structure
+  type(int_tide_CS),        pointer       :: int_tide_CSp !< Internal tide control structure
   integer,                  intent(out)   :: halo_TS !< The halo size of tracer points that must be
                                                   !! valid for the calculations in set_diffusivity.
   logical,                  intent(out)   :: double_diffuse !< This indicates whether some version