__devexit functions are discarded when CONFIG_HOTPLUG
is not set, so the symbol needs to be referenced carefully.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>