slimbus: core: Set fwnode for a device when setting of_node

slimbus: core: Set fwnode for a device when setting of_node

When setting the of_node for a newly created device, also set the
fwnode. This allows fw_devlink feature to work for slimbus devices.

Also, remove some unnecessary NULL checks. The functions in question
already do NULL checks.

Signed-off-by: Saravana Kannan <saravanak@google.com>
[Srini: removed unnecessary NULL check from other patch]
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20200511151334.362-2-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>