nfsd: Fix unnecessary deny bits in NFSv4 ACL

The group deny entries end up denying tcy even though tcy was just
allowed by the allow entry. This appears to be due to:
	ace->access_mask = mask_from_posix(deny, flags);
instead of:
	ace->access_mask = deny_mask_from_posix(deny, flags);

Denying a previously allowed bit has no effect, so this shouldn't affect
behavior, but it's ugly.

Signed-off-by: Frank Filz <ffilzlnx@us.ibm.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>