bitesize: work with different versions of awk and bash

This patch tries to fix following bitesize issues,

1. Error flooding messages when array index value is negative.
2. the smax in gawk was treated as string, that cause bug when
   perf return zero IO count.

Signed-off-by: Yong Yang <yangoliver@gmail.com>

disk/bitesize

@@ -85,8 +85,11 @@ sectors=(${buckets[*]})
 ((max_i = ${#buckets[*]} - 1))
 while (( i <= max_i )); do
 	(( sectors[$i] = ${sectors[$i]} * 1024 / $secsz ))
-	if (( i && ${sectors[$i]} <= ${sectors[$i - 1]} )); then
-		die "ERROR: bucket list must increase in size."
+	# avoid negative array index errors for old version bash
+	if (( i > 0 ));then
+		if (( ${sectors[$i]} <= ${sectors[$i - 1]} )); then
+			die "ERROR: bucket list must increase in size."
+		fi
 	fi
 	(( i++ ))
 done
@@ -136,7 +139,8 @@ echo
 echo "$stat" | awk -v tpoint=$tpoint -v max_i=$max_i -v most=$most '
 	function star(sval, smax, swidth) {
 		stars = ""
-		if (smax == 0) return ""
+		# using int could avoid error on gawk
+		if (int(smax) == 0) return ""
 		for (si = 0; si < (swidth * sval / smax); si++) {
 			stars = stars "#"
 		}