schemast: proper float field conversion

[zeevmoney]

ent is using Float and not Float64 as the float64 field, this fix handles it.

// Float returns a new Field with type float64.
func Float(name string) *float64Builder {
	return &float64Builder{&Descriptor{
		Name: name,
		Info: &TypeInfo{Type: TypeFloat64},
	}}
}