sched: Mark sched_clock() as notrace

The core ftrace code (trace_clock_local) calls sched_clock()
directly, so we don't want to recurisvely trigger the ftrace
code.  Rather than update every sched_clock() definition, tag
the prototype for everyone as notrace.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <1260407223-10900-1-git-send-email-vapier@gentoo.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>