const fixup for ARB_direct_state_access ClearNamedFramebufferfv value parameter (#334)

diff --git a/extensions/ARB/ARB_direct_state_access.txt b/extensions/ARB/ARB_direct_state_access.txt
index f58f30b..8e9e746 100644
--- a/extensions/ARB/ARB_direct_state_access.txt
+++ b/extensions/ARB/ARB_direct_state_access.txt
@@ -220,7 +220,7 @@
                                   int drawbuffer, const uint *value);
 
     void ClearNamedFramebufferfv(uint framebuffer, enum buffer,
-                                 int drawbuffer, float *value);
+                                 int drawbuffer, const float *value);
 
     void ClearNamedFramebufferfi(uint framebuffer, enum buffer,
                                  int drawbuffer, float depth, int stencil);