perf symbols: Correct final kernel map guesses

If a 32bit userspace perf is running on a 64bit kernel, the end of the final
map in the kernel would incorrectly be set to 2^32-1 rather than 2^64-1.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1290658375-10342-1-git-send-email-imunsie@au1.ibm.com>
Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>