perf & kvm: Clean up some of the guest profiling callback API details

Fix some build bug and programming style issues:

 - use valid C
 - fix up various style details

Signed-off-by: Zhang Yanmin <yanmin_zhang@linux.intel.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Sheng Yang <sheng@linux.intel.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: oerg Roedel <joro@8bytes.org>
Cc: Jes Sorensen <Jes.Sorensen@redhat.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: Zachary Amsden <zamsden@redhat.com>
Cc: zhiteng.huang@intel.com
Cc: tim.c.chen@intel.com
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
LKML-Reference: <1271729638.2078.624.camel@ymzhang.sh.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>