of: platform: Demote kernel-doc abuse

Fixes the following W=1 kernel build warning(s):

 drivers/of/platform.c:298: warning: Function parameter or member 'lookup' not described in 'of_dev_lookup'
 drivers/of/platform.c:298: warning: Function parameter or member 'np' not described in 'of_dev_lookup'

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Frank Rowand <frowand.list@gmail.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Anton Vorontsov <anton@enomsg.org>
Cc: Colin Cross <ccross@android.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: benh@kernel.crashing.org
Cc: devicetree@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210318104036.3175910-4-lee.jones@linaro.org