drm/amd: Copy entire structure in amdgpu_acpi_get_backlight_caps()

As new members are introduced to the structure copying the entire
structure will help avoid missing them.

Reviewed-by: Alex Hung <alex.hung@amd.com>
Link: https://lore.kernel.org/r/20250228185145.186319-2-mario.limonciello@amd.com


Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>