ent/entc: corrently reference default value on migrate generation

Summary:
Migration incorrectly generated field default value on storage key inclusion.

Example Field:
```
field.String("tenant").
  StorageKey("organization").
  Default("fb-test"),
```
Generated default of:
```
// DefaultTenant holds the default value on creation for the tenant field.
DefaultTenant = descTenant.Default.(string)
```
But migration references non existent default (storage key is used):
```
{Name: "organization", Type: field.TypeString, Default: user.DefaultOrganization},
```

Reviewed By: a8m

Differential Revision: D17578898

fbshipit-source-id: afca92ac3f34c16100c868a10d0a480139bf4262

examples/o2o2types/ent/card.go

@@ -16,7 +16,7 @@ import (
 
 // Card is the model entity for the Card schema.
 type Card struct {
-	config
+	config `json:"-"`
 	// ID of the ent.
 	ID int `json:"id,omitempty"`
 	// Expired holds the value of the "expired" field.

examples/o2o2types/ent/user.go

@@ -15,7 +15,7 @@ import (
 
 // User is the model entity for the User schema.
 type User struct {
-	config
+	config `json:"-"`
 	// ID of the ent.
 	ID int `json:"id,omitempty"`
 	// Age holds the value of the "age" field.

examples/o2o2types/ent/user_update.go

@@ -37,12 +37,17 @@ func (uu *UserUpdate) Where(ps ...predicate.User) *UserUpdate {
 // SetAge sets the age field.
 func (uu *UserUpdate) SetAge(i int) *UserUpdate {
 	uu.age = &i
+	uu.addage = nil
 	return uu
 }
 
 // AddAge adds i to age.
 func (uu *UserUpdate) AddAge(i int) *UserUpdate {
-	uu.addage = &i
+	if uu.addage == nil {
+		uu.addage = &i
+	} else {
+		*uu.addage += i
+	}
 	return uu
 }
 
@@ -204,12 +209,17 @@ type UserUpdateOne struct {
 // SetAge sets the age field.
 func (uuo *UserUpdateOne) SetAge(i int) *UserUpdateOne {
 	uuo.age = &i
+	uuo.addage = nil
 	return uuo
 }
 
 // AddAge adds i to age.
 func (uuo *UserUpdateOne) AddAge(i int) *UserUpdateOne {
-	uuo.addage = &i
+	if uuo.addage == nil {
+		uuo.addage = &i
+	} else {
+		*uuo.addage += i
+	}
 	return uuo
 }