GPencil: Use proper enumerator type

Was using GpencilModifierType in type definition,
but rest of usage was using values from GpencilModifierTypeType.

source/blender/blenkernel/BKE_gpencil_modifier.h

@@ -102,7 +102,7 @@ typedef struct GpencilModifierTypeInfo {
 	/* The size of the modifier data type, used by allocation. */
 	int struct_size;
 
-	GpencilModifierType type;
+	GpencilModifierTypeType type;
 	GpencilModifierTypeFlag flags;