autofs4: pass mode to autofs4_get_inode() explicitly

In all cases we'd set inf->mode to know value just before
passing it to autofs4_get_inode().  That kills the need
to store it in autofs_info and pass it to autofs_init_ino()

Acked-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>