drm/i915/gt: Exercise lrc_wa_ctx initialisation failure

Inject a fault into lrc_init_wa_ctx() to ensure that we can tolerate a
failure to construct the workarounds.

v2: Avoid mentioning an error for fault-injection, other CI will
complain about the dmesg spam.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210109114453.27798-1-chris@chris-wilson.co.uk