mesa: return INVALID_VALUE from VertexAttribDivisor if index out of range

All the other range checks on index already return the proper error,
INVALID_VALUE.

Fixes gles3conform's instanced_arrays_invalid test.
Reviewed-by: Paul Berry <stereotype441@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/main/varray.c

@@ -1137,7 +1137,7 @@ _mesa_VertexAttribDivisor(GLuint index, GLuint divisor)
    }
 
    if (index >= ctx->Const.VertexProgram.MaxAttribs) {
-      _mesa_error(ctx, GL_INVALID_ENUM, "glVertexAttribDivisor(index = %u)",
+      _mesa_error(ctx, GL_INVALID_VALUE, "glVertexAttribDivisor(index = %u)",
                   index);
       return;
    }