added missing returns (fluent setter)

[rasstislav]

No description provided.

[GuySartorelli]

Thank you for submitting this.
In the future can you please supply a bit more information? There's nothing inherent about this PR that shows why they should be fluent methods. I ended up finding that setValue() is defined in DBField and the phpdoc says to return $this:

silverstripe-framework/src/ORM/FieldType/DBField.php

Lines 238 to 244 in 7ea25bf

	* @return $this
	*/
	public function setValue($value, $record = null, $markChanged = true)
	{
	$this->value = $value;
	return $this;
	}

[rasstislav]

Thanks @GuySartorelli :)