dma-mapping: benchmark: Restore padding to ensure uABI remained consistent

dma-mapping: benchmark: Restore padding to ensure uABI remained consistent

commit 23ee8a2563a0f24cf4964685ced23c32be444ab8 upstream.

The padding field in the structure was previously reserved to
maintain a stable interface for potential new fields, ensuring
compatibility with user-space shared data structures.
However,it was accidentally removed by tiantao in a prior commit,
which may lead to incompatibility between user space and the kernel.

This patch reinstates the padding to restore the original structure
layout and preserve compatibility.

Fixes: 8ddde07a3d28 ("dma-mapping: benchmark: extract a common header file for map_benchmark definition")
Cc: stable@vger.kernel.org
Acked-by: Barry Song <baohua@kernel.org>
Signed-off-by: Qinxin Xia <xiaqinxin@huawei.com>
Reported-by: Barry Song <baohua@kernel.org>
Closes: https://lore.kernel.org/lkml/CAGsJ_4waiZ2+NBJG+SCnbNk+nQ_ZF13_Q5FHJqZyxyJTcEop2A@mail.gmail.com/
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20251028120900.2265511-2-xiaqinxin@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>