drivers: regulator: fix reference count underflow

Fixes regulator reference count underflow and adds error code
for attempting to disable an already disabled regulator

(cherry picked from commit 95622e4)

Original-Signed-off-by: Vladislav Litvinov <vladislav.litvinov@nordicsemi.no>
GitOrigin-RevId: 95622e4
Cr-Build-Id: 8740696253239544497
Cr-Build-Url: https://cr-buildbucket.appspot.com/build/8740696253239544497
Change-Id: I290a61f998561472f103a8c6152a848a50ab539f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5760302
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>
Tested-by: Fabio Baltieri <fabiobaltieri@google.com>
Reviewed-by: Fabio Baltieri <fabiobaltieri@google.com>
Commit-Queue: Fabio Baltieri <fabiobaltieri@google.com>

drivers/regulator/regulator_common.c

@@ -183,12 +183,14 @@ int regulator_disable(const struct device *dev)
 	(void)k_mutex_lock(&data->lock, K_FOREVER);
 #endif
 
-	data->refcnt--;
+	if (data->refcnt > 0) {
+		data->refcnt--;
 
-	if (data->refcnt == 0) {
-		ret = api->disable(dev);
-		if (ret < 0) {
-			data->refcnt++;
+		if (data->refcnt == 0) {
+			ret = api->disable(dev);
+			if (ret < 0) {
+				data->refcnt++;
+			}
 		}
 	}