Documentation: pps: fix spelling mistake

Signed-off-by: Eric Engestrom <[e-mail]>
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/pps/pps.txt

···
     };
 
 and then calling the function pps_register_source() in your
-intialization routine as follows:
+initialization routine as follows:
 
     source = pps_register_source(&pps_ktimer_info,
 			PPS_CAPTUREASSERT | PPS_OFFSETASSERT);