[Why]
Need a check for NULL pointer access for ddc pin and aux engine.

[How]
Adding a check for ddc pin and aux engine accesses.
Reviewed-by: NJimmy Kizito <jimmy.kizito@amd.com>
Acked-by: NMikita Lipski <mikita.lipski@amd.com>
Signed-off-by: NMeenakshikumar Somasundaram <meenakshikumar.somasundaram@amd.com>
Tested-by: NDaniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>