tracing/fastboot: fix bootgraph.pl initcall name regexp

The regexp used to match the start and the end of an initcall
are matching only on [a-zA-Z\_]. This rules out initcalls with
a number in them. This patch is fixing that.

Signed-off-by: Arnaud Patard <apatard@mandriva.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>