drm/i915/gem: use spinlock_t instead of struct spinlock

spinlock_t is one case where the typedef is to be preferred over struct
spinlock.

Fixes: 42fb60de ("drm/i915/gem: Don't leak non-persistent requests on changing engines")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200217184219.15325-1-jani.nikula@intel.com

drivers/gpu/drm/i915/gem/i915_gem_context_types.h

@@ -181,7 +181,7 @@ struct i915_gem_context {
 	char name[TASK_COMM_LEN + 8];
 
 	struct {
-		struct spinlock lock;
+		spinlock_t lock;
 		struct list_head engines;
 	} stale;
 };