x/sequencers: simplify bond update allowed to take sequencer

[danwt]

dymension/x/sequencer/keeper/msg_server_increase_bond.go

Lines 43 to 47 in acd9d13

	// check if the sequencer already exists
	sequencer, found := k.GetSequencer(ctx, senderAddress)
	if !found {
	return types.Sequencer{}, types.ErrUnknownSequencer
	}

should take sequencer as arg, not return it

#1031 (comment)

[danwt]

superseded by #1328