staging: wilc1000: look for rtc_clk clock

If rtc_clk is provided from DT, use it and enable it.
This is optional.
The signal may be hardcoded and no need to be requested,
but if DT provides it, use it.

Signed-off-by: Eugen Hristev <[e-mail]>
Acked-by: Ajay Singh <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/wilc1000/wilc_sdio.c

···
  * All rights reserved.
  */
 
+#include <linux/clk.h>
 #include <linux/mmc/sdio_func.h>
 #include <linux/mmc/host.h>
 
···
 	wilc->dev = &func->dev;
 	wilc->gpio_irq = gpio;
 
+	wilc->rtc_clk = devm_clk_get(&func->card->dev, "rtc_clk");
+	if (PTR_ERR_OR_ZERO(wilc->rtc_clk) == -EPROBE_DEFER)
+		return -EPROBE_DEFER;
+	else if (!IS_ERR(wilc->rtc_clk))
+		clk_prepare_enable(wilc->rtc_clk);
+
 	dev_info(&func->dev, "Driver Initializing success\n");
 	return 0;
 }
···
 	/* free the GPIO in module remove */
 	if (wilc->gpio_irq)
 		gpiod_put(wilc->gpio_irq);
+
+	if (!IS_ERR(wilc->rtc_clk))
+		clk_disable_unprepare(wilc->rtc_clk);
+
 	wilc_netdev_cleanup(wilc);
 }
 
···
 
 	dev_info(dev, "sdio suspend\n");
 	chip_wakeup(wilc);
+
+	if (!IS_ERR(wilc->rtc_clk))
+		clk_disable_unprepare(wilc->rtc_clk);
 
 	if (wilc->suspend_event) {
 		host_sleep_notify(wilc);

drivers/staging/wilc1000/wilc_wfi_netdevice.h

···
 	int io_type;
 	s8 mac_status;
 	struct gpio_desc *gpio_irq;
+	struct clk *rtc_clk;
 	bool initialized;
 	int dev_irq_num;
 	int close;