intel: Fix memory leak in case of renderbuffer bad format

Signed-off-by: Brian Paul <brianp@vmware.com>

src/mesa/drivers/dri/intel/intel_fbo.c

@@ -385,6 +385,7 @@ intel_create_renderbuffer(GLenum intFormat)
    default:
       _mesa_problem(NULL,
                     "Unexpected intFormat in intel_create_renderbuffer");
+      _mesa_free(irb);
       return NULL;
    }