perf session: create_kernel_maps should use ->host_machine

Using machines__create_kernel_maps(..., HOST_KERNEL_ID) it would create
another machine instance for the host machine, and since 1f626bc3 we have
it out of the machines rb_tree.

Fix it by using machine__create_kernel_maps(&self->host_machine)
directly.

Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>