Multires: Store modifier pointer for subdivide

Allows to access its settings during the subdivision process.

source/blender/blenkernel/intern/multires_reshape.h

@@ -39,6 +39,7 @@ typedef struct MultiresReshapeContext {
   /* NOTE: Only available when context is initialized from object. */
   struct Depsgraph *depsgraph;
   struct Object *object;
+
   struct MultiresModifierData *mmd;
 
   /* Base mesh from original object.

source/blender/blenkernel/intern/multires_reshape_util.c

@@ -218,6 +218,7 @@ bool multires_reshape_context_create_from_subdivide(MultiresReshapeContext *resh
 
   Mesh *base_mesh = (Mesh *)object->data;
 
+  reshape_context->mmd = mmd;
   reshape_context->base_mesh = base_mesh;
 
   reshape_context->subdiv = multires_reshape_create_subdiv(NULL, object, mmd);