sleep: let's turn off the RTC alarm time ASAP

Let's be a tiny bit more careful here.

Also, let's rearrange things to simplify them a bit, and to not use "r"
outside of its immediate scope of validity.

src/sleep/sleep.c

@@ -246,22 +246,22 @@ static int execute_s2h(usec_t hibernate_delay_sec) {
         if (r < 0)
                 return r;
 
-        r = rtc_read_time(&cmp_time);
+        /* Reset RTC right-away */
+        r = rtc_write_wake_alarm(0);
         if (r < 0)
                 return r;
 
-        /* reset RTC */
-        r = rtc_write_wake_alarm(0);
+        r = rtc_read_time(&cmp_time);
         if (r < 0)
                 return r;
 
         log_debug("Woke up at %"PRIu64, cmp_time);
 
-        /* if woken up after alarm time, hibernate */
-        if (cmp_time >= wake_time)
-                r = execute(hibernate_modes, hibernate_states);
+        if (cmp_time < wake_time) /* We woke up before the alarm time, we are done. */
+                return 0;
 
-        return r;
+        /* If woken up after alarm time, hibernate */
+        return execute(hibernate_modes, hibernate_states);
 }
 
 static int help(void) {