drm/i915/guc: Change GEM_WARN_ON to guc_err to prevent taints in CI

This warning was supposed to catch a harmless issue, but changing to
guc_error should prevent kernel taints in CI runs.

Signed-off-by: Jesus Narvaez <jesus.narvaez@intel.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240808204943.911727-1-jesus.narvaez@intel.com