vringh: define the stride used for translation

Define a macro to be reused in the different parts of the code.

Useful for the next patches where we add more arrays to manage also
translations with user VA.
Suggested-by: Eugenio Perez Martin <eperezma@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20230404131326.44403-5-sgarzare@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vhost/vringh.c

@@ -1141,13 +1141,15 @@ static int iotlb_translate(const struct vringh *vrh,
 	return ret;
 }
 
+#define IOTLB_IOV_STRIDE 16
+
 static inline int copy_from_iotlb(const struct vringh *vrh, void *dst,
 				  void *src, size_t len)
 {
 	u64 total_translated = 0;
 
 	while (total_translated < len) {
-		struct bio_vec iov[16];
+		struct bio_vec iov[IOTLB_IOV_STRIDE];
 		struct iov_iter iter;
 		u64 translated;
 		int ret;
@@ -1180,7 +1182,7 @@ static inline int copy_to_iotlb(const struct vringh *vrh, void *dst,
 	u64 total_translated = 0;
 
 	while (total_translated < len) {
-		struct bio_vec iov[16];
+		struct bio_vec iov[IOTLB_IOV_STRIDE];
 		struct iov_iter iter;
 		u64 translated;
 		int ret;