driver core: make subsys_dev_iter_exit() static

The function subsys_dev_iter_exit() is not used outside of
drivers/base/bus.c so make it static to that file and remove the global
export.

Reviewed-by: Rafael J. Wysocki <rafael@kernel.org>
Link: https://lore.kernel.org/r/20230109175810.2965448-5-gregkh@linuxfoundation.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>