make df more readable

Filesystem             Size   Used   Free   Blksize
/dev                   164M    32K   164M   4096
/system                442M   117M   325M   4096
/cache                 492M     8M   483M   4096
/data                  984M    59M   925M   4096
/mnt/sdcard             12G    27M    12G   32768

Change-Id: I9a84b7b84ae528ee5cf0b1e92a8bee032b87703b
1 file changed