lavapipe: Fix struct initialization

Fix defect reported by Coverity Scan.

Evaluation order violation (EVALUATION_ORDER)
write_write_typo: In box.x = box.x = copy->imageOffset.x, box.x is written twice with the same value.

Fixes: 9e9d90c6c3 ("lavapipe: VK_EXT_host_image_copy")
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Konstantin Seurer <konstantin.seurer@gmail.com>
Reviewed-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24531>

src/gallium/frontends/lavapipe/lvp_image.c

@@ -672,10 +672,10 @@ lvp_CopyImageToMemoryEXT(VkDevice _device, const VkCopyImageToMemoryInfoEXT *pCo
    for (unsigned i = 0; i < pCopyImageToMemoryInfo->regionCount; i++) {
       const VkImageToMemoryCopyEXT *copy = &pCopyImageToMemoryInfo->pRegions[i];
       struct pipe_box box = {
-         box.x = copy->imageOffset.x,
-         box.y = copy->imageOffset.y,
-         box.width = copy->imageExtent.width,
-         box.height = copy->imageExtent.height,
+         .x = copy->imageOffset.x,
+         .y = copy->imageOffset.y,
+         .width = copy->imageExtent.width,
+         .height = copy->imageExtent.height,
          .depth = 1,
       };
       switch (image->bo->target) {