Align interface with actual use.

* The second dimension of rect has indeed as many dimensions as
  appropriate for the array being written, i.e. 2 or 3 depending on
  whether a z-axis exists.

src/cdi.h

@@ -431,8 +431,8 @@ void    streamReadVarSlicePart(int streamID, int varID, int levelID, int varType
 void    streamReadVarSlice(int streamID, int varID, int levelID, double data[], SizeType *nmiss);
 void    streamReadVarSliceF(int streamID, int varID, int levelID, float data[], SizeType *nmiss);
 
-void    streamWriteVarChunk(int streamID, int varID, const int rect[3][2], const double data[], SizeType nmiss);
-void    streamWriteVarChunkF(int streamID, int varID, const int rect[3][2], const float data[], SizeType nmiss);
+void    streamWriteVarChunk(int streamID, int varID, const int rect[][2], const double data[], SizeType nmiss);
+void    streamWriteVarChunkF(int streamID, int varID, const int rect[][2], const float data[], SizeType nmiss);
 
 
 // STREAM record I/O routines (sequential access)