Fix suffix property doc typo: "prefix" -> "suffix"

(cherry picked from commit ae067413a592b0c30c5cd99263de97c2f63c274d)

doc/classes/SpinBox.xml

@@ -45,7 +45,7 @@
 			Adds the specified [code]prefix[/code] string before the numerical value of the [SpinBox].
 		</member>
 		<member name="suffix" type="String" setter="set_suffix" getter="get_suffix" default="&quot;&quot;">
-			Adds the specified [code]prefix[/code] string after the numerical value of the [SpinBox].
+			Adds the specified [code]suffix[/code] string after the numerical value of the [SpinBox].
 		</member>
 	</members>
 	<constants>