The definition of rpc_count_iostats_metrics() is borked.

Reported by: Jim Davis <jim.epost@gmail.com>
Fixes: d67ae825 ("pnfs/flexfiles: Add the FlexFile Layout Driver")
Cc: Tom Haynes <thomas.haynes@primarydata.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>