xen: update PV-device interface headers

Update the Xen PV-device interface headers in order to avoid undefined
behavior with flexible arrays being defined with one array element.

Reported-by: Pry Mar <[e-mail]>
Signed-off-by: Juergen Gross <[e-mail]>
Acked-by: Stefano Stabellini <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Juergen Gross <[e-mail]>

include/xen/interface/io/displif.h

···
 
 struct xendispl_page_directory {
 	grant_ref_t gref_dir_next_page;
-	grant_ref_t gref[1]; /* Variable length */
+	grant_ref_t gref[];
 };
 
 /*

include/xen/interface/io/ring.h

···
     RING_IDX req_prod, req_event;                                       \
     RING_IDX rsp_prod, rsp_event;                                       \
     uint8_t __pad[48];                                                  \
-    union __name##_sring_entry ring[1]; /* variable-length */           \
+    union __name##_sring_entry ring[];                                  \
 };                                                                      \
                                                                         \
 /* "Front" end's private variables */                                   \

include/xen/interface/io/sndif.h

···
 
 struct xensnd_page_directory {
 	grant_ref_t gref_dir_next_page;
-	grant_ref_t gref[1]; /* Variable length */
+	grant_ref_t gref[];
 };
 
 /*