drivers: ethernet: stm32: avoid unnecessary casts, silence warnings

There is no need to use *_cmp_raw() functions here, all they do is cast the
pointers to in(6)_addr* and call the non-raw functions. Additionally, this
fixes a warning for the net_ipv6_addr_cmp_raw() call, which didn't cast the
arguments correctly.

Signed-off-by: Armin Brauns <armin.brauns@embedded-solutions.at>