perf tools: Fix buildid cache handling of kallsyms with kcore

When kallsyms is used with kcore the dso long_name becomes the kcore
file name.  That prevents the buildid cache from caching kallsyms.
(There is no support at present for caching kcore).  Fix by changing it
so that the kallsyms name is used in that case instead.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1379009959-28046-1-git-send-email-adrian.hunter@intel.com


[ Kept 'struct foo' pointer as first parameter of foo__ prefixed functions ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>