perf symbols: Do not include libgen.h

That causes us to end up using the XPG version of basename which can
modify it's argument.
Signed-off-by: David S. Miller <davem@davemloft.net>
Link: http://lkml.kernel.org/r/20120327.000301.1122788061724345175.davem@davemloft.netSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/symbol.c

 #include <dirent.h>
 #include <errno.h>
-#include <libgen.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>