rtc: zynqmp: Fix optional clock name property

Clock description in DT binding introduced by commit f69060c14431
("dt-bindings: rtc: zynqmp: Add clock information") is talking about "rtc"
clock name but driver is checking "rtc_clk" name instead.
Because clock is optional property likely in was never handled properly by
the driver.

Fixes: 07dcc6f9c762 ("rtc: zynqmp: Add calibration set and get support")
Signed-off-by: Michal Simek <[e-mail]>
Cc: [e-mail]
Reviewed-by: Peter Korsgaard <[e-mail]>
Link: https://lore.kernel.org/r/cd5f[e-mail]
Signed-off-by: Alexandre Belloni <[e-mail]>

drivers/rtc/rtc-zynqmp.c

···
 		return ret;
 	}
 
-	/* Getting the rtc_clk info */
-	xrtcdev->rtc_clk = devm_clk_get_optional(&pdev->dev, "rtc_clk");
+	/* Getting the rtc info */
+	xrtcdev->rtc_clk = devm_clk_get_optional(&pdev->dev, "rtc");
 	if (IS_ERR(xrtcdev->rtc_clk)) {
 		if (PTR_ERR(xrtcdev->rtc_clk) != -EPROBE_DEFER)
 			dev_warn(&pdev->dev, "Device clock not found.\n");