pci: Change error_report to assert(3)

Asserts are used for developer bugs. As registering a bar of the wrong
size is not something that should be possible for a user to achieve,
this is a developer bug.

While here, use the more obvious helper function.

Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
Message-Id: <20201015181411.89104-1-ben.widawsky@intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

hw/pci/pci.c

@@ -1151,11 +1151,7 @@ void pci_register_bar(PCIDevice *pci_dev, int region_num,
 
     assert(region_num >= 0);
     assert(region_num < PCI_NUM_REGIONS);
-    if (size & (size-1)) {
-        error_report("ERROR: PCI region size must be pow2 "
-                    "type=0x%x, size=0x%"FMT_PCIBUS"", type, size);
-        exit(1);
-    }
+    assert(is_power_of_2(size));
 
     r = &pci_dev->io_regions[region_num];
     r->addr = PCI_BAR_UNMAPPED;