NFS: nfs4_bitmask_adjust() must not change the server global bitmasks

As currently set, the calls to nfs4_bitmask_adjust() will end up
overwriting the contents of the nfs_server cache_consistency_bitmask
field.
The intention here should be to modify a private copy of that mask in
the close/delegreturn/write arguments.

Fixes: 76bd5c01 ("NFSv4: make cache consistency bitmask dynamic")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>