vfs: correct the comments of vfs_*() helpers

correct the comments of vfs_*() helpers in fs/namei.c, including:
1. vfs_create()
2. vfs_mknod()
3. vfs_mkdir()
4. vfs_rmdir()
5. vfs_symlink()

All of them come from the same commit:
6521f891

 "namei: prepare for idmapped mounts"

The @dentry is actually the dentry of child directory rather than
base directory(parent directory), and thus the @dir has to be
modified due to the change of @dentry.

Signed-off-by: Congjie Zhou <zcjie0802@qq.com>
Link: https://lore.kernel.org/r/tencent_2FCF6CC9E10DC8A27AE58A5A0FE4FCE96D0A@qq.com


Signed-off-by: Christian Brauner <brauner@kernel.org>