media: media_device_enum_links32: clean a reserved field

In v4l2-compliance utility, test MEDIA_IOC_ENUM_ENTITIES
will check whether reserved field of media_links_enum filled
with zero.

However, for 32 bit program, the reserved field is missing
copy from kernel space to user space in media_device_enum_links32
function.

This patch adds the cleaning a reserved field logic in
media_device_enum_links32 function.

Signed-off-by: Jungo Lin <jungo.lin@mediatek.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>