vpnor: Rename generate-squashfs to generate-tar

The tool refernced in table.hpp is renamed to generate-tar.
Update the comment in code.

Change-Id: I67f75dbe5018ab71d65f87ee14093c3972eb5846
Signed-off-by: Lei YU <mine260309@gmail.com>

vpnor/table.hpp

@@ -79,7 +79,7 @@ namespace partition
  *
  *  Generates virtual PNOR partition table upon construction. Reads
  *  the PNOR information generated by this tool :
- *  github.com/openbmc/openpower-pnor-code-mgmt/blob/master/generate-squashfs,
+ *  github.com/openbmc/openpower-pnor-code-mgmt/blob/master/generate-tar,
  *  which generates a minimalistic table-of-contents (toc) file and
  *  individual files to represent various partitions that are of interest -
  *  these help form the "virtual" PNOR, which is typically a subset of the full