perf tools: Fix a compiling error in util/map.c

perf tools: Fix a compiling error in util/map.c

This patch fix a compile warning taken as error:

	CC util/map.o
	cc1: warnings being treated as errors
	util/map.c: In function ‘map__fprintf_dsoname’:
	util/map.c:240: error: ‘dsoname’ may be used uninitialized in this function
	make: *** [util/map.o] Error 1

Signed-off-by: Feng Tang <feng.tang@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1346053107-11946-3-git-send-email-feng.tang@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>