clk: at91: Fix a return value in case of error

If 'clk_hw_register()' fails, it is likely that we expect to return an
error instead of a valid pointer (which would mean success).

Fix commit f5644f10dcfb ("clk: at91: Migrate to clk_hw based registration
and OF APIs")

Signed-off-by: Christophe JAILLET <[e-mail]>
Signed-off-by: Stephen Boyd <[e-mail]>

drivers/clk/at91/clk-programmable.c

···
 	ret = clk_hw_register(NULL, &prog->hw);
 	if (ret) {
 		kfree(prog);
-		hw = &prog->hw;
+		hw = ERR_PTR(ret);
 	}
 
 	return hw;