nfsd: use C99 struct initializers

Eliminate 56 sparse warnings like this one:

fs/nfsd/nfs4xdr.c:1331:15: warning: obsolete array initializer, use C99 syntax

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Neil Brown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>