interconnect: imx: Remove a useless test

'dn' can't be NULL here, it is tested just the line above.
Remove this useless test.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/20201206121322.29434-1-christophe.jaillet@wanadoo.fr


Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>