unsquashfs: fix error statement

Forgot to update error message when function was renamed.

Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
unsquashfs: add support for displaying compression options

Add support to display the compression options used to
compress the filesystem in -stat.

Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>