perf tools: Fix const char type propagation

The following perf build warnings/errors in function
argument types:

  builtin-sched.c:1894: warning: passing argument 1 of 'sort_dimension__add' discards qualifiers from pointer target type
  util/trace-event-parse.c:685: warning: passing argument 2 of 'read_expected' discards qualifiers from pointer target type
  util/trace-event-parse.c:741: warning: passing argument 4 of 'test_type_token' discards qualifiers from pointer target type
  util/trace-event-parse.c:706: warning: passing argument 2 of 'read_expected_item' discards qualifiers from pointer target type

... trigger because older GCC is not able to prove that
sort_dimension__add() does not change the string.

Some goes for test_type_token().

Fix this by improving type consistency.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <20091005131729.78444bfb.randy.dunlap@oracle.com>
[ Also remove ugly type cast now unnecessary. ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>