CVE-2026-98785: drm/amd/display: check dc_state_create_copy() for NULL in dm_suspend

In the Linux kernel, the following vulnerability has been resolved: drm/amd/display: check dc_state_create_copy() for NULL in dm_suspend dc_state_create_copy() can return NULL on allocation failure. dm_suspend() only conditionally skips dm_gpureset_toggle_interrupts() and continues execution, returning success. dm_resume() then dereferences the NULL cached_dc_state in link_enc_cfg_copy() and the following dc_state->stream_count loop, crashing during GPU reset recovery. Return -ENOMEM immediately if the copy fails, so the caller aborts suspend instead of leaving a NULL cached state for resume. (cherry picked from commit 84b6d7932fdd2857795a257f9f258562a3cddcab)