clocksource: dbx500-prcmu: comment cleanup

Remove references to the deprecated DB5500 platform.
Acked-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NFabio Baltieri <fabio.baltieri@linaro.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

drivers/clocksource/clksrc-dbx500-prcmu.c

@@ -10,7 +10,7 @@
  * DBx500-PRCMU Timer
  * The PRCMU has 5 timers which are available in a always-on
  * power domain.  We use the Timer 4 for our always-on clock
- * source on DB8500 and Timer 3 on DB5500.
+ * source on DB8500.
  */
 #include <linux/clockchips.h>
 #include <linux/clksrc-dbx500-prcmu.h>