perf: Version String fix, using kernel version

Changes the Perf --version string such that it shows the kernel
version as suggested by Ingo as follows:

That way the perf that comes with v2.6.34 will be:

  perf version v2.6.34

while interim versions will have the version of the interim
kernel - for example:

 perf version v2.6.35-rc4-70-g39ef13a

This functionality was already in the perf version generator
file except that it was looking for a .git in the perf directory
instead of the kernel directory.

Signed-off-by: Thavidu Ranatunga <tharan@au1.ibm.com>
Acked-by: Ian Munsie <imunsie@au1.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <1278316815-6099-1-git-send-email-tharan@au1.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>