[PATCH][next] drm: xlnx: zynqmp_disp: Avoid -Wflex-array-member-not-at-end warning

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

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

Use the TRAILING_OVERLAP() helper to fix the following warning:

drivers/gpu/drm/xlnx/zynqmp_disp.c:102:41: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

This helper creates a union between a flexible-array member (FAM)
and a set of members that would otherwise follow it. This overlays
the trailing members onto the FAM while preserving the original
memory layout.

Lastly, the static_assert() ensures the alignment between the FAM and
struct data_chunk sgl; is not inadvertently changed, and it's
intentionally placed inmediately after the related structure (that is,
no blank line in between),

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/gpu/drm/xlnx/zynqmp_disp.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/xlnx/zynqmp_disp.c b/drivers/gpu/drm/xlnx/zynqmp_disp.c
index 9a8f38230cb4..05807c7a93d7 100644
--- a/drivers/gpu/drm/xlnx/zynqmp_disp.c
+++ b/drivers/gpu/drm/xlnx/zynqmp_disp.c
@@ -99,9 +99,14 @@ struct zynqmp_disp_format {
  */
 struct zynqmp_disp_layer_dma {
 	struct dma_chan *chan;
-	struct dma_interleaved_template xt;
-	struct data_chunk sgl;
+
+	/* Must be last as it ends in a flexible-array member. */
+	TRAILING_OVERLAP(struct dma_interleaved_template, xt, sgl,
+		struct data_chunk sgl;
+	);
 };
+static_assert(offsetof(struct zynqmp_disp_layer_dma, xt.sgl) ==
+	      offsetof(struct zynqmp_disp_layer_dma, sgl));
 
 /**
  * struct zynqmp_disp_layer_info - Static layer information
-- 
2.51.0