slimbus: ngd: Fix build error on x86

on non DT platforms like x86 of_match_node is set to NULL, dereferencing
directly would throw an error.
Fix this by doing this in two steps, get the match then the data.

Reported-by: Greg KH <gregkh@linuxfoundation.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>