drm/amd/display: Deallocate DML memory if allocation fails

[Why]
When DC state create DML memory allocation fails, memory is not
deallocated subsequently, resulting in uninitialized structure
that is not NULL.

[How]
Deallocate memory if DML memory allocation fails.

Reviewed-by: Joshua Aberback <joshua.aberback@amd.com>
Signed-off-by: Jerry Zuo <jerry.zuo@amd.com>
Signed-off-by: Chris Park <chris.park@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>