make use of anon_inode_getfile_fmode()

["fallen through the cracks" misc stuff]

A bunch of anon_inode_getfile() callers follow it with adjusting
->f_mode; we have a helper doing that now, so let's make use
of it.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Link: https://lore.kernel.org/r/20250118014434.GT1977892@ZenIV


Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>