Uppercase variable overlooked in last commit.

Originally committed as revision 9777 to svn://svn.ffmpeg.org/ffmpeg/trunk

libpostproc/Makefile

@@ -2,7 +2,7 @@
 include ../config.mak
 
 # Overload incdir, postproc include files go in a different directory.
-incdir=$(prefix)/include/postproc
+INCDIR=$(prefix)/include/postproc
 
 EXTRALIBS := -L$(BUILD_ROOT)/libavutil -lavutil$(BUILDSUF) $(EXTRALIBS)