drm/amd/display: Handle dml allocation failure to avoid crash

In the Linux kernel, the following vulnerability has been resolved:

drm/amd/display: Handle dml allocation failure to avoid crash

[Why]

In the case where a dml allocation fails for any reason, the

current state's dml contexts would no longer be valid. Then

subsequent calls dc_state_copy_internal would shallow copy

invalid memory and if the new state was released, a double

free would occur.

[How]

Reset dml pointers in new_state to NULL and avoid invalid

pointer

(cherry picked from commit bcafdc61529a48f6f06355d78eb41b3aeda5296c)