hw/pci/pci_host.c: Avoid shifting left into sign bit

Add U suffix to avoid undefined behaviour.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

hw/pci/pci_host.c

@@ -142,8 +142,9 @@ static uint64_t pci_host_data_read(void *opaque,
 {
     PCIHostState *s = opaque;
     uint32_t val;
-    if (!(s->config_reg & (1 << 31)))
+    if (!(s->config_reg & (1U << 31))) {
         return 0xffffffff;
+    }
     val = pci_data_read(s->bus, s->config_reg | (addr & 3), len);
     PCI_DPRINTF("read addr " TARGET_FMT_plx " len %d val %x\n",
                 addr, len, val);