drm/amdgpu: fix UBSAN warning in kv_dpm.c

Adds bounds check for sumo_vid_mapping_entry.

Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3392


Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org