perf kmem: Resolve kernel symbols again

Due to the assumption in perf_session__new that the kernel maps would be
created using the fake PERF_RECORD_MMAP event in a perf.data file 'perf
kmem --stat caller', that doesn't have such event, ends up not being
able to resolve the kernel addresses.

Fix it by calling perf_session__create_kernel_maps() in __cmd_kmem().

LKML-Reference: <new-submission>
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>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-kmem.c

@@ -489,6 +489,9 @@ static int __cmd_kmem(void)
 	if (session == NULL)
 		return -ENOMEM;
 
+	if (perf_session__create_kernel_maps(session) < 0)
+		goto out_delete;
+
 	if (!perf_session__has_traces(session, "kmem record"))
 		goto out_delete;