rtc: snvs: fix an incorrect check of return value

BugLink: http://bugs.launchpad.net/bugs/1765010

[ Upstream commit 75892900 ]

Function devm_regmap_init_mmio() returns an ERR_PTR on error. However,
in function snvs_rtc_probe() its return value is checked against NULL.
This patch fixes it by checking the return value with IS_ERR().
Signed-off-by: Pan Bian <bianpan2016@163.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

drivers/rtc/rtc-snvs.c

@@ -257,7 +257,7 @@ static int snvs_rtc_probe(struct platform_device *pdev)
 		of_property_read_u32(pdev->dev.of_node, "offset", &data->offset);
 	}
 
-	if (!data->regmap) {
+	if (IS_ERR(data->regmap)) {
 		dev_err(&pdev->dev, "Can't find snvs syscon\n");
 		return -ENODEV;
 	}