mmc: sunxi: Use devm_reset_control_get_optional() for reset control

[ Upstream commit 9e71c589 ]

The reset control for the sunxi mmc controller is optional. Some
newer platforms (sun6i, sun8i, sun9i) have it, while older ones
(sun4i, sun5i, sun7i) don't.

Use the properly stubbed _optional version so the driver does not
fail to compile when RESET_CONTROLLER=n.

This patch also adds a check for deferred probing on the reset
control.
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Cc: <stable@vger.kernel.org> # 3.16+
Acked-by: David Lanzendörfer <david.lanzendoerfer@o2s.ch>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

drivers/mmc/host/sunxi-mmc.c

@@ -909,7 +909,9 @@ static int sunxi_mmc_resource_request(struct sunxi_mmc_host *host,
 		return PTR_ERR(host->clk_mmc);
 	}
 
-	host->reset = devm_reset_control_get(&pdev->dev, "ahb");
+	host->reset = devm_reset_control_get_optional(&pdev->dev, "ahb");
+	if (PTR_ERR(host->reset) == -EPROBE_DEFER)
+		return PTR_ERR(host->reset);
 
 	ret = clk_prepare_enable(host->clk_ahb);
 	if (ret) {