mount_pseudo(): drop 'name' argument, switch to d_make_root()

Once upon a time we used to set ->d_name of e.g. pipefs root
so that d_path() on pipes would work.  These days it's
completely pointless - dentries of pipes are not even connected
to pipefs root.  However, mount_pseudo() had set the root
dentry name (passed as the second argument) and callers
kept inventing names to pass to it.  Including those that
didn't *have* any non-root dentries to start with...

All of that had been pointless for about 8 years now; it's
time to get rid of that cargo-culting...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/block_dev.c

@@ -837,7 +837,7 @@ static struct dentry *bd_mount(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *data)
 {
 	struct dentry *dent;
-	dent = mount_pseudo(fs_type, "bdev:", &bdev_sops, NULL, BDEVFS_MAGIC);
+	dent = mount_pseudo(fs_type, &bdev_sops, NULL, BDEVFS_MAGIC);
 	if (!IS_ERR(dent))
 		dent->d_sb->s_iflags |= SB_I_CGROUPWB;
 	return dent;