AFS: Fix silly characters in a comment

Fix silly characters in a comment in AFS code (some weird characters replaced
the word 'flag' some point way back).

Reported-by:  <viro@ZenIV.linux.org.uk>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>