nvmem: core: Check input parameter for NULL in nvmem_unregister()

nvmem_unregister() frees resources and standard pattern is to allow
caller to not care if it's NULL or not. This will reduce burden on
the callers to perform this check.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20220220151527.17216-4-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/core.c

@@ -903,7 +903,8 @@ static void nvmem_device_release(struct kref *kref)
  */
 void nvmem_unregister(struct nvmem_device *nvmem)
 {
-	kref_put(&nvmem->refcnt, nvmem_device_release);
+	if (nvmem)
+		kref_put(&nvmem->refcnt, nvmem_device_release);
 }
 EXPORT_SYMBOL_GPL(nvmem_unregister);