xen/arm: pci: fix -Wtype-limits warning in pci-host-common.c

When building with EXTRA_CFLAGS_XEN_CORE="-Wtype-limits", we observe the
following warning:

arch/arm/pci/pci-host-common.c: In function ‘pci_host_common_probe’:
arch/arm/pci/pci-host-common.c:238:26: warning: comparison is always false due to limited range of data type [-Wtype-limits]
  238 |     if ( bridge->segment < 0 )
      |                          ^

This is due to bridge->segment being an unsigned type. Fix it by introducing a
new variable of signed type to use in the condition.

Fixes: 6ec9176d94 ("xen/arm: PCI host bridge discovery within XEN on ARM")
Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
Reviewed-by: Rahul Singh <rahul.singh@arm.com<mailto:rahul.singh@arm.com>>

xen/arch/arm/pci/pci-host-common.c

@@ -214,6 +214,7 @@ int pci_host_common_probe(struct dt_device_node *dev,
     struct pci_host_bridge *bridge;
     struct pci_config_window *cfg;
     int err;
+    int domain;
 
     if ( dt_device_for_passthrough(dev) )
         return 0;
@@ -234,12 +235,13 @@ int pci_host_common_probe(struct dt_device_node *dev,
     bridge->cfg = cfg;
     bridge->ops = &ops->pci_ops;
 
-    bridge->segment = pci_bus_find_domain_nr(dev);
-    if ( bridge->segment < 0 )
+    domain = pci_bus_find_domain_nr(dev);
+    if ( domain < 0 )
     {
         printk(XENLOG_ERR "Inconsistent \"linux,pci-domain\" property in DT\n");
         BUG();
     }
+    bridge->segment = domain;
     pci_add_host_bridge(bridge);
 
     return 0;