net: bcmgenet: Remove the unused function

The function dmadesc_get_addr() is defined in the bcmgenet.c file, but
not called elsewhere, so remove this unused function.

drivers/net/ethernet/broadcom/genet/bcmgenet.c:120:26: warning: unused function 'dmadesc_get_addr'.

Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=3401
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Link: https://lore.kernel.org/r/20221209033723.32452-1-jiapeng.chong@linux.alibaba.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>