docs/devel: fix description of OBJECT_DECLARE_SIMPLE_TYPE

Since 30b5707c (qom: Remove module_obj_name parameter from
OBJECT_DECLARE* macros) we don't need the additional two parameters.
Fix the documentation.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220725140520.515340-13-alex.bennee@linaro.org>

docs/devel/qom.rst

@@ -292,8 +292,7 @@ in the header file:
 .. code-block:: c
    :caption: Declaring a simple type
 
-   OBJECT_DECLARE_SIMPLE_TYPE(MyDevice, my_device,
-                              MY_DEVICE, DEVICE)
+   OBJECT_DECLARE_SIMPLE_TYPE(MyDevice, MY_DEVICE)
 
 This is equivalent to the following: