net: ethernet: mtk_wed: Fix NULL vs IS_ERR() bug in mtk_wed_get_memory_region()

We recently changed this from using devm_ioremap() to using
devm_ioremap_resource() and unfortunately the former returns NULL while
the latter returns error pointers.  The check for errors needs to be
updated as well.

Fixes: e27dba19 ("net: Use of_reserved_mem_region_to_resource{_byname}() for "memory-region"")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/87c10dbd-df86-4971-b4f5-40ba02c076fb@sabinyo.mountain


Signed-off-by: Jakub Kicinski <kuba@kernel.org>