smc91x: add __init markings to smc_drv_probe()

The smc_drv_probe() is the platform_driver probe function and it is only
called during init.  Further, it calls smc_probe() which is marked as __init
already.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>