kernel: drm/i915: Fix NULL pointer dereference in capture_engine

In the Linux kernel, the following vulnerability has been resolved: drm/i915: Fix NULL pointer dereference in captureengine When the intelcontext structure contains NULL, it raises a NULL pointer dereference error in drminfo. cherry picked from commit 754302a5bc1bd8fd3b7d85c168b0a1af6d4bba4d...