mesa: don't set _ClampFragmentColor to TRUE if it has no effect

This should reduce shader recompilations with drivers that emulate fragment
color clamping, because we want the clamping to be enabled only if there is
a signed normalized or floating-point colorbuffer.

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

src/mesa/state_tracker/st_atom_shader.c

@@ -86,8 +86,7 @@ update_fp( struct st_context *st )
 
    /* _NEW_FRAG_CLAMP */
    key.clamp_color = st->clamp_frag_color_in_shader &&
-                     st->ctx->Color._ClampFragmentColor &&
-                     !st->ctx->DrawBuffer->_IntegerColor;
+                     st->ctx->Color._ClampFragmentColor;
 
    st->fp_variant = st_get_fp_variant(st, stfp, &key);