PM: Add "RTC" to PM trace time stamps to avoid confusion

Some users are apparently confused by dmesg output from
read_magic_time(), which looks like "real" time and date.
Add the "RTC" string to time stamps printed by read_magic_time() to
avoid that confusion.
Reported-by: Justin P. Mattock <justinmattock@gmail.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

drivers/base/power/trace.c

@@ -112,7 +112,7 @@ static unsigned int read_magic_time(void)
 	unsigned int val;
 
 	get_rtc_time(&time);
-	pr_info("Time: %2d:%02d:%02d  Date: %02d/%02d/%02d\n",
+	pr_info("RTC time: %2d:%02d:%02d, date: %02d/%02d/%02d\n",
 		time.tm_hour, time.tm_min, time.tm_sec,
 		time.tm_mon + 1, time.tm_mday, time.tm_year % 100);
 	val = time.tm_year;				/* 100 years */