staging/wilc1000: use more regular probing

So far, my patches tried to do equivalent conversions of the
existing code.  This one goes beyond that by restructuring
how the devices get probed. In particular, the spi driver
no longer creates the netdev until the device is probed,
and I've removed the global wilc_sdio_func and wilc_spi_dev
variables in favor of retrieving them from the wilc_dev
variable that will eventually get passed through all functions
instead of using a global.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>