Squashfs: add corruption check for type in squashfs_readdir()

We read the type field from disk.  This value should be sanity
checked for correctness to avoid an out of bounds access when
reading the squashfs_filetype_table array.

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

diff --cc fs/squashfs/dir.c
Simple merge

diff --cc fs/squashfs/squashfs_fs.h
Simple merge