drm/amd/display: fix null pointer dereference

While setting cursor position in case of mpo,
input_pixel_processor is not available for underlay,
hence add check of the same to avoid null pointer
access issue.

Signed-off-by: Shirish S <shirish.s@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_stream.c

@@ -288,7 +288,7 @@ bool dc_stream_set_cursor_position(
 			pos_cpy.enable = false;
 
 
-		if (ipp->funcs->ipp_cursor_set_position != NULL)
+		if (ipp !=NULL && ipp->funcs->ipp_cursor_set_position != NULL)
 			ipp->funcs->ipp_cursor_set_position(ipp, &pos_cpy, &param);
 
 		if (mi != NULL && mi->funcs->set_cursor_position != NULL)