eth: dpaa2-mac: remove a dead-code NULL check on fwnode parent

Since commit 4e30e98c

 ("dpaa2-mac: return -EPROBE_DEFER from dpaa2_mac_open in case the fwnode is not set")
@parent can't be NULL after the if. It's either the address
of the ->fwnode of @dpmacs or @fwnode in case of ACPI.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20220506200029.852310-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>