Fix a typo in highres.txt

A small patch for the highres timers documentation:

Signed-off-by: Will newton <[e-mail]>
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/hrtimers/highres.txt

···
 event devices are used to provide local CPU functionality such as process
 accounting, profiling, and high resolution timers.
 
-The management layer assignes one or more of the folliwing functions to a clock
+The management layer assigns one or more of the following functions to a clock
 event device:
       - system global periodic tick (jiffies update)
       - cpu local update_process_times