anv: Return correct result in EnumeratePhysicalDevices

If pPhysicalDevices is too small for all physical devices,
the driver must return VK_INCOMPLETE.
Since only a single physical device is supported, this is only the case
when pPhysicalDeviceCount == 0 && pPhysicalDevices != NULL.

Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/intel/vulkan/anv_device.c

@@ -385,6 +385,8 @@ VkResult anv_EnumeratePhysicalDevices(
    } else if (*pPhysicalDeviceCount >= 1) {
       pPhysicalDevices[0] = anv_physical_device_to_handle(&instance->physicalDevice);
       *pPhysicalDeviceCount = 1;
+   } else if (*pPhysicalDeviceCount < instance->physicalDeviceCount) {
+      return VK_INCOMPLETE;
    } else {
       *pPhysicalDeviceCount = 0;
    }