extract_storage: fix a bug on selecting modules directory name

extract_storage: fix a bug on selecting modules directory name

In the sub-script, which is externally invoked by this script,
there was a little bug like "cd /lib/modules/*storage/".
This has been working if there's only 1 directory under /lib/modules.
But after upgrading kernel 3.4.23 to 3.4.51, there could be 2 different
directories, because ANDBD package could be possibly depending on
the older version.

To avoid such situations, set the kernel modules directory just the
same as its kernel version.