perf symbols: Fix up map end too on modular kernels with no modules installed

In 2161db96 we stopped failing when not finding modules when
asked too, but then the kernel maps (just one, for vmlinux)
wasn't having its ->end field correctly set up, so symbols were
not being found for the vmlinux map because its range was 0-0.

Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1266702793-29434-1-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>