hrtimers: doc cleanup

It has:
a tense correction(led->leads);
a typo(unevitably->inevitably);

Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/timers/hrtimers.txt

@@ -28,9 +28,9 @@ several reasons why such integration is hard/impossible:
 
 - the unpredictable [O(N)] overhead of cascading leads to delays which
   necessitate a more complex handling of high resolution timers, which
-  in turn decreases robustness. Such a design still led to rather large
+  in turn decreases robustness. Such a design still leads to rather large
   timing inaccuracies. Cascading is a fundamental property of the timer
-  wheel concept, it cannot be 'designed out' without unevitably
+  wheel concept, it cannot be 'designed out' without inevitably
   degrading other portions of the timers.c code in an unacceptable way.
 
 - the implementation of the current posix-timer subsystem on top of