x86: pat.c more trivial changes

 - add BUG statement to catch invalid start and end parameters
 - No need to track the actual type in both req_type and actual_type --
   keep req_type unchanged.
 - removed (IMHO) superfluous comments

Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Cc: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Suresh B Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>