Fix options for command: free

Right now, free -k is no different from free -m and free -g. free -b
gives the output for free -h. This patch fixes the above problem.

Signed-off-by: Nehal J Wani <nehaljw.kkd1@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>