drm/i915/guc: Fix blocked context accounting

Prior to this patch the blocked context counter was cleared on
init_sched_state (used during registering a context & resets) which is
incorrect. This state needs to be persistent or the counter can read the
incorrect value resulting in scheduling never getting enabled again.

Fixes: 62eaf0ae ("drm/i915/guc: Support request cancellation")
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: <stable@vger.kernel.org>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210909164744.31249-2-matthew.brost@intel.com