iommufd/iommufd_private.h: Avoid -Wflex-array-member-not-at-end warning

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

Move the conflicting declaration to the end of the corresponding
structure. Notice that struct iommufd_vevent is a flexible
structure, this is a structure that contains a flexible-array
member.

Fix the following warning:

drivers/iommu/iommufd/iommufd_private.h:621:31: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Link: https://patch.msgid.link/r/aRHOAwpATIE0oajj@kspp
Signed-off-by: "Gustavo A. R. Silva" <[email protected]>
Fixes: e36ba5a ("iommufd: Add IOMMUFD_OBJ_VEVENTQ and IOMMUFD_CMD_VEVENTQ_ALLOC")
Reviewed-by: Kevin Tian <[email protected]>
Reviewed-by: Nicolin Chen <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>

Author: GustavoARSilva

drivers/iommu/iommufd/iommufd_private.h

@@ -614,14 +614,16 @@ struct iommufd_veventq {
 	struct iommufd_eventq common;
 	struct iommufd_viommu *viommu;
 	struct list_head node; /* for iommufd_viommu::veventqs */
-	struct iommufd_vevent lost_events_header;
 
 	enum iommu_veventq_type type;
 	unsigned int depth;
 
 	/* Use common.lock for protection */
 	u32 num_events;
 	u32 sequence;
+
+	/* Must be last as it ends in a flexible-array member. */
+	struct iommufd_vevent lost_events_header;
 };
 
 static inline struct iommufd_veventq *