fix : update miss where's condition when primary key use "<-:create" tag

[ghost]

• [] Do only one thing
• [] Non breaking API changes
• [] Tested

What did this pull request do?

fix:update miss where condition for #4734

when use update and primary key field use <-:create tag , maybe result in error.

User Case Description

Demo code:

//model.go
type User struct {
	ID   uint   `gorm:"column:id;<-:create"`
	Name string `gorm:"column:name"`
}

//dal.go
user := model.User{ID: 1, Name: "king"}
tx.Debug().Save(&user)
if tx.Error != nil {
	fmt.Printf("Failed, got error: %v \n", tx.Error)
}

Run result:

[0.135ms] [rows:0] UPDATE `users` SET `name`="king"
Failed, got error: WHERE conditions required 

Except result:

[0.172ms] [rows:0] UPDATE `users` SET `name`="king" WHERE `id` = 1

[jinzhu]

thank you for your PR.