benchmark.bash: OSX dd does not support "K" postfix

tests/canonical-benchmarks.bash

@@ -12,6 +12,7 @@ if [ $# -ne 1 ]; then
 	exit 1
 fi
 
+# cd to TESTDIR
 cd "$1"
 
 TGZ=/tmp/linux-3.0.tar.gz
@@ -28,7 +29,7 @@ function etime {
 }
 
 echo -n "WRITE: "
-dd if=/dev/zero of=zero bs=128K count=2000 2>&1 | tail -n 1
+dd if=/dev/zero of=zero bs=131072 count=2000 2>&1 | tail -n 1
 rm zero
 sleep 1
 echo -n "UNTAR: "