drm/i915: Wrap our timer_list.expires checking

Refactor our timer_list.expires checking into its own timer_active()
helper.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210107123541.17153-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_utils.c

@@ -87,7 +87,7 @@ bool i915_error_injected(void)
 
 void cancel_timer(struct timer_list *t)
 {
-	if (!READ_ONCE(t->expires))
+	if (!timer_active(t))
 		return;
 
 	del_timer(t);

drivers/gpu/drm/i915/i915_utils.h

@@ -438,9 +438,14 @@ static inline void __add_taint_for_CI(unsigned int taint)
 void cancel_timer(struct timer_list *t);
 void set_timer_ms(struct timer_list *t, unsigned long timeout);
 
+static inline bool timer_active(const struct timer_list *t)
+{
+	return READ_ONCE(t->expires);
+}
+
 static inline bool timer_expired(const struct timer_list *t)
 {
-	return READ_ONCE(t->expires) && !timer_pending(t);
+	return timer_active(t) && !timer_pending(t);
 }
 
 /*