net: aquantia: Fix aq_vec_isr_legacy() return value

The irqreturn_t type is an enum or an unsigned int in GCC.  That
creates to problems because it can't detect if the
self->aq_hw_ops->hw_irq_read() call fails and at the end the function
always returns IRQ_HANDLED.

drivers/net/ethernet/aquantia/atlantic/aq_vec.c:316 aq_vec_isr_legacy() warn: unsigned 'err' is never less than zero.
drivers/net/ethernet/aquantia/atlantic/aq_vec.c:329 aq_vec_isr_legacy() warn: always true condition '(err >= 0) => (0-u32max >= 0)'

Fixes: 970a2e98 ("net: ethernet: aquantia: Vector operations")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Igor Russkikh <igor.russkikh@aquantia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/aquantia/atlantic/aq_vec.c

@@ -306,15 +306,13 @@ irqreturn_t aq_vec_isr_legacy(int irq, void *private)
 {
 	struct aq_vec_s *self = private;
 	u64 irq_mask = 0U;
-	irqreturn_t err = 0;
+	int err;
 
-	if (!self) {
-		err = -EINVAL;
-		goto err_exit;
-	}
+	if (!self)
+		return IRQ_NONE;
 	err = self->aq_hw_ops->hw_irq_read(self->aq_hw, &irq_mask);
 	if (err < 0)
-		goto err_exit;
+		return IRQ_NONE;
 
 	if (irq_mask) {
 		self->aq_hw_ops->hw_irq_disable(self->aq_hw,
@@ -322,11 +320,10 @@ irqreturn_t aq_vec_isr_legacy(int irq, void *private)
 		napi_schedule(&self->napi);
 	} else {
 		self->aq_hw_ops->hw_irq_enable(self->aq_hw, 1U);
-		err = IRQ_NONE;
+		return IRQ_NONE;
 	}
 
-err_exit:
-	return err >= 0 ? IRQ_HANDLED : IRQ_NONE;
+	return IRQ_HANDLED;
 }
 
 cpumask_t *aq_vec_get_affinity_mask(struct aq_vec_s *self)