greybus: spi: add device_type field to device config

Add device_type field in device config operation to get the type of
device and try to expose less the kernel internal over greybus.
This include the spidev, spi-nor will fetch the correct nor id over
jede and a modalias that will have the previous behavior (name will set
the driver to be loaded).

As at it, fix a trivial error path and return immediately.

Tested: using gbsim and confirming that a spidev and mtd device were
created.

Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>