NFSv4: remove obviously bogus comparison from decode_getacl

We just set *acl_len to zero, and attrlen is unsigned, so this comparison
is clearly bogus.  I have no idea what I was thinking.

Fixes a bug that caused getacl to fail over krb5p.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>