net: ethernet: adi: Fix invalid parent name length

MII_BUS_ID_SIZE is larger than MAX_PHYS_ITEM_ID_LEN
so we use the former here to set the parent port id.

Fixes: bc93e19d

 ("net: ethernet: adi: Add ADIN1110 support")
Signed-off-by: Alexandru Tachici <alexandru.tachici@analog.com>
Link: https://lore.kernel.org/r/20220922063049.10388-1-alexandru.tachici@analog.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>