Only truncate file types that can be truncated on minixfs.

Only regular files, directories and symbolic links can have any
blocks allocated to them - other types of files have different
metadata in their inodes and should not get to the truncation
paths. Enforce this in fs/minix/inode.c.

Without this, deleting a block or character device can cause
minix filesystem corruption. Noted by Konstantin Boldyshev.

fs/minix/inode.c

@@ -547,6 +547,8 @@ int minix_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *sta
  */
 void minix_truncate(struct inode * inode)
 {
+	if (!(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)))
+		return;
 	if (INODE_VERSION(inode) == MINIX_V1)
 		V1_minix_truncate(inode);
 	else