tg3: Remove redundant assignments

The assignment of err will be overwritten next, so this statement
should be deleted.

The clang_analyzer complains as follows:

drivers/net/ethernet/broadcom/tg3.c:5506:2: warning:

Value stored to 'expected_sg_dig_ctrl' is never read
Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: luo penghao <luo.penghao@zte.com.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/tg3.c

@@ -5503,7 +5503,6 @@ static bool tg3_setup_fiber_hw_autoneg(struct tg3 *tp, u32 mac_status)
 	int workaround, port_a;
 
 	serdes_cfg = 0;
-	expected_sg_dig_ctrl = 0;
 	workaround = 0;
 	port_a = 1;
 	current_link_up = false;