perf symbols: Support to read compressed module from build-id cache

The commit c00c48fc6e6e ("perf symbols: Preparation for compressed
kernel module support") added support for compressed kernel modules but
it only supports system path DSOs.  When a dso is read from build-id
cache, its filename doesn't end with ".gz" but has build-id.  In this
case, we should fallback to the original dso->name.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1422518843-25818-2-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>