[PATCH][next] xen/pci: Avoid -Wflex-array-member-not-at-end warning

["Gustavo A. R. Silva" <gustavoars@kernel.org>]

Use the `DEFINE_RAW_FLEX()` helper for an on-stack definition of
a flexible structure where the size of the flexible-array member
is known at compile-time, and refactor the rest of the code,
accordingly.

So, with this, fix the following warning:

drivers/xen/pci.c:48:55: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/xen/pci.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/drivers/xen/pci.c b/drivers/xen/pci.c
index 72d4e3f193af..a2facd8f7e51 100644
--- a/drivers/xen/pci.c
+++ b/drivers/xen/pci.c
@@ -44,15 +44,11 @@ static int xen_add_device(struct device *dev)
 	}
 #endif
 	if (pci_seg_supported) {
-		struct {
-			struct physdev_pci_device_add add;
-			uint32_t pxm;
-		} add_ext = {
-			.add.seg = pci_domain_nr(pci_dev->bus),
-			.add.bus = pci_dev->bus->number,
-			.add.devfn = pci_dev->devfn
-		};
-		struct physdev_pci_device_add *add = &add_ext.add;
+		DEFINE_RAW_FLEX(struct physdev_pci_device_add, add, optarr, 1);
+
+		add->seg = pci_domain_nr(pci_dev->bus);
+		add->bus = pci_dev->bus->number;
+		add->devfn = pci_dev->devfn;
 
 #ifdef CONFIG_ACPI
 		acpi_handle handle;
-- 
2.34.1