net: ethernet: oa_tc6: mdiobus->parent initialized with NULL

net: ethernet: oa_tc6: mdiobus->parent initialized with NULL

As "dev" pointer in oa_tc6 structure is never initialized,
mbiobus->parent was initialized with NULL.  This change
fixes it by initializing it with device pointer of spi.

Fixes: 8f9bf857e43b ("net: ethernet: oa_tc6: implement internal PHY initialization")
Signed-off-by: Selvamani Rajagopal <Selvamani.Rajagopal@onsemi.com>
Link: https://patch.msgid.link/20260611-level-trigger-v5-2-4533a9e85ce2@onsemi.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>