wal: fix "unconvert" warnings
wal: fix "unconvert" warnings

Signed-off-by: Gyuho Lee <3454051ee3341eb69bdf6fca40899cdad4d86496@gmail.com>

sebrandon1/etcd,vimalk78/etcd,rnaveiras/etcd,mqliang/etcd,mqliang/etcd,coreos/etcd,ajityagaty/etcd,ajityagaty/etcd,joshix/etcd,joshix/etcd,ajityagaty/etcd,bdarnell/etcd,mqliang/etcd,coreos/etcd,rnaveiras/etcd,etcd-io/etcd,dannysauer/etcd,etcd-io/etcd,xiang90/etcd,vimalk78/etcd,gyuho/etcd,bdarnell/etcd,etcd-io/etcd,cockroachdb/etcd,mkumatag/etcd,sebrandon1/etcd,li-ang/etcd,mkumatag/etcd,xiang90/etcd,gyuho/etcd,sinsharat/etcd,glevand/coreos--etcd,glevand/coreos--etcd,rnaveiras/etcd,li-ang/etcd,sinsharat/etcd,cockroachdb/etcd,dannysauer/etcd,mkumatag/etcd