vDPA/ifcvf: Fix pci_read_config_byte() return code handling

ifcvf_init_hw() uses pci_read_config_byte() that returns
PCIBIOS_* codes. The error handling, however, assumes the codes are
normal errnos because it checks for < 0.
Convert the error check to plain non-zero check.

Fixes: 5a2414bc ("virtio: Intel IFC VF driver for VDPA")
Signed-off-by: Yuan Can <yuancan@huawei.com>
Message-Id: <20241017013812.129952-1-yuancan@huawei.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Zhu Lingshan <lingshan.zhu@kernel.org>