watchdog: xen: don't clear is_active when xen_wdt_stop() failed

xen_wdt_release() shouldn't clear is_active even when the watchdog
didn't get stopped (which by itself shouldn't happen, but let's return
a proper error in this case rather than adding a BUG() upon hypercall
failure).
Signed-off-by: NJan Beulich <jbeulich@suse.com>
Signed-off-by: NWim Van Sebroeck <wim@iguana.be>

drivers/watchdog/xen_wdt.c

@@ -132,15 +132,17 @@ static int xen_wdt_open(struct inode *inode, struct file *file)
 
 static int xen_wdt_release(struct inode *inode, struct file *file)
 {
+	int err = 0;
+
 	if (expect_release)
-		xen_wdt_stop();
+		err = xen_wdt_stop();
 	else {
 		pr_crit("unexpected close, not stopping watchdog!\n");
 		xen_wdt_kick();
 	}
-	is_active = false;
+	is_active = err;
 	expect_release = false;
-	return 0;
+	return err;
 }
 
 static ssize_t xen_wdt_write(struct file *file, const char __user *data,