net: aquantia: fix unsigned numvecs comparison with less than zero

From: Colin Ian King <colin.king@canonical.com>

This was originally mistakenly submitted to net-next. Resubmitting to net.

The comparison of numvecs < 0 is always false because numvecs is a u32
and hence the error return from a failed call to pci_alloc_irq_vectores
is never detected.  Fix this by using the signed int ret to handle the
error return and assign numvecs to err.

Detected by CoverityScan, CID#1468650 ("Unsigned compared against 0")

Fixes: a09bd81b ("net: aquantia: Limit number of vectors to actually allocated irqs")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Igor Russkikh <igor.russkikh@aquantia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>