timers: Adjust a kernel-doc comment

Those three warnings can easily solved by using :: to indicate a
code block:

	./kernel/time/timer.c:1259: WARNING: Unexpected indentation.
	./kernel/time/timer.c:1261: WARNING: Unexpected indentation.
	./kernel/time/timer.c:1262: WARNING: Block quote ends without a blank line; unexpected unindent.

While here, align the lines at the block.
Signed-off-by: NMauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Linux Doc Mailing List <linux-doc@vger.kernel.org>
Cc: Mauro Carvalho Chehab <mchehab@infradead.org>
Cc: John Stultz <john.stultz@linaro.org>
Link: https://lkml.kernel.org/r/f02e6a0ce27f3b5e33415d92d07a40598904b3ee.1525684985.git.mchehab%2Bsamsung@kernel.org

kernel/time/timer.c

@@ -1251,7 +1251,7 @@ EXPORT_SYMBOL(try_to_del_timer_sync);
  *
  * Note: For !irqsafe timers, you must not hold locks that are held in
  *   interrupt context while calling this function. Even if the lock has
- *   nothing to do with the timer in question.  Here's why:
+ *   nothing to do with the timer in question.  Here's why::
  *
  *    CPU0                             CPU1
  *    ----                             ----