egl: Include stddef.h in generated source

Required for NULL macro used throughout the generated file.

Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>

src/egl/generate/gen_egl_dispatch.py

@@ -131,6 +131,7 @@ def generateSource(functions):
     text = ""
     text += '#include "egldispatchstubs.h"\n'
     text += '#include "g_egldispatchstubs.h"\n'
+    text += '#include <stddef.h>\n'
     text += "\n"
 
     for (func, eglFunc) in functions: