tg3: Remove residual error handling in tg3_suspend

As of now, tg3_power_down_prepare always ends with success, but
the error handling code from former tg3_set_power_state call is still here.

This code became unreachable in commit c866b7e ("tg3: Do not use
legacy PCI power management").

Remove (now unreachable) error handling code for simplification and change
tg3_power_down_prepare to a void function as its result is no more checked.

Signed-off-by: Nikita Kiryushin <kiryushin@ancud.ru>
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240401191418.361747-1-kiryushin@ancud.ru
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/ethernet/broadcom/tg3.c

@@ -4019,7 +4019,7 @@ static int tg3_power_up(struct tg3 *tp)
 
 static int tg3_setup_phy(struct tg3 *, bool);
 
-static int tg3_power_down_prepare(struct tg3 *tp)
+static void tg3_power_down_prepare(struct tg3 *tp)
 {
 	u32 misc_host_ctrl;
 	bool device_should_wake, do_low_power;
@@ -4263,7 +4263,7 @@ static int tg3_power_down_prepare(struct tg3 *tp)
 
 	tg3_ape_driver_state_change(tp, RESET_KIND_SHUTDOWN);
 
-	return 0;
+	return;
 }
 
 static void tg3_power_down(struct tg3 *tp)
@@ -18084,7 +18084,6 @@ static int tg3_suspend(struct device *device)
 {
 	struct net_device *dev = dev_get_drvdata(device);
 	struct tg3 *tp = netdev_priv(dev);
-	int err = 0;
 
 	rtnl_lock();
 
@@ -18108,32 +18107,11 @@ static int tg3_suspend(struct device *device)
 	tg3_flag_clear(tp, INIT_COMPLETE);
 	tg3_full_unlock(tp);
 
-	err = tg3_power_down_prepare(tp);
-	if (err) {
-		int err2;
-
-		tg3_full_lock(tp, 0);
-
-		tg3_flag_set(tp, INIT_COMPLETE);
-		err2 = tg3_restart_hw(tp, true);
-		if (err2)
-			goto out;
-
-		tg3_timer_start(tp);
-
-		netif_device_attach(dev);
-		tg3_netif_start(tp);
-
-out:
-		tg3_full_unlock(tp);
-
-		if (!err2)
-			tg3_phy_start(tp);
-	}
+	tg3_power_down_prepare(tp);
 
 unlock:
 	rtnl_unlock();
-	return err;
+	return 0;
 }
 
 static int tg3_resume(struct device *device)