net: dm9051: Use PTR_ERR_OR_ZERO() to simplify code

Use the standard error pointer macro to shorten the code and simplify.

Signed-off-by: Yu Liao <liaoyu15@huawei.com>
Link: https://lore.kernel.org/r/20230822021455.205101-2-liaoyu15@huawei.com


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