net: bcmgenet: re-remove bcmgenet_hfb_add_filter

This function was originally removed by Baoyou Xie in
commit e2072600 ("net: bcmgenet: remove unused function in
bcmgenet.c") to prevent a build warning.

Some of the functions removed by Baoyou Xie are now used for
WAKE_FILTER support so his commit was reverted, but this function
is still unused and the kbuild test robot dutifully reported the
warning.

This commit once again removes the remaining unused hfb functions.

Fixes: 14da1510 ("Revert "net: bcmgenet: remove unused function in bcmgenet.c"")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Doug Berger <opendmb@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>