thermal: db8500_cpufreq_cooling: remove usage of IS_ERR_OR_NULL()

This patch changes the driver to avoid the usage of IS_ERR_OR_NULL()
macro. This macro can lead to dangerous results, like returning
success (0) during a failure scenario (NULL pointer handling).

The case present in this driver can be translated to a simple
check for IS_ERR(), as the cpufreq_cooling_register() returns
either a valid pointer or an ERR_PTR().

Cc: Zhang Rui <[e-mail]>
Cc: Russell King <[e-mail]>
Cc: Grant Likely <[e-mail]>
Cc: Rob Herring <[e-mail]>
Cc: Hongbo Zhang <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Eduardo Valentin <[e-mail]>
Acked-by: Fabio Baltieri <[e-mail]>
Signed-off-by: Zhang Rui <[e-mail]>

drivers/thermal/db8500_cpufreq_cooling.c

···
 	cpumask_set_cpu(0, &mask_val);
 	cdev = cpufreq_cooling_register(&mask_val);
 
-	if (IS_ERR_OR_NULL(cdev)) {
+	if (IS_ERR(cdev)) {
 		dev_err(&pdev->dev, "Failed to register cooling device\n");
 		return PTR_ERR(cdev);
 	}