[gegl] build: patch up breakage introduced in prior commit

[Øyvind "pippin" Kolås <ok src gnome org>]

commit 6638803d37159f1f4b67f7ab542bfff58841594d
Author: Øyvind Kolås <pippin gimp org>
Date:   Mon Sep 10 14:24:23 2018 +0200

    build: patch up breakage introduced in prior commit
    
    Ooops, the header files for buffer are installed from the parent dir.

 gegl/Makefile.am | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gegl/Makefile.am b/gegl/Makefile.am
index e0e1972c5..95e7a089d 100644
--- a/gegl/Makefile.am
+++ b/gegl/Makefile.am
@@ -79,7 +79,7 @@ GEGL_public_HEADERS = \
        gegl-op.h                       \
        gegl-plugin.h                   \
        buffer/gegl-tile.h \
-       buffer/gegl-buffer-cl-iterator.h
+       opencl/gegl-buffer-cl-iterator.h
 
 GEGL_sources = \
        gegl-algorithms.c \