perf bench mem: Use USEC_PER_SEC

Following kernel practices, using linux/time64.h

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-xdtmguafva17wp023sxojiib@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/bench/mem-functions.c

@@ -21,6 +21,7 @@
 #include <string.h>
 #include <sys/time.h>
 #include <errno.h>
+#include <linux/time64.h>
 
 #define K 1024
 
@@ -89,7 +90,7 @@ static u64 get_cycles(void)
 
 static double timeval2double(struct timeval *ts)
 {
-	return (double)ts->tv_sec + (double)ts->tv_usec / (double)1000000;
+	return (double)ts->tv_sec + (double)ts->tv_usec / (double)USEC_PER_SEC;
 }
 
 #define print_bps(x) do {						\