perf_counter: Make call graph option consistent

perf record uses -g for logging call graph data but perf report
uses -c to print call graph data. Be consistent and use -g
everywhere for call graph data.

Also update the help text to reflect the current default -
fractal,0.5

Signed-off-by: Anton Blanchard <anton@samba.org>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20090716104817.803604373@samba.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>