Always set up a negative ACL cache entry if the inode can't have ACLs.
That behaves much better than doing this check inside ->check_acl.

Also remove the left over MAY_NOT_BLOCK check.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>