drm/i915: Use BIT() for computing the engine's flag

Since the engine's flag is just the bit of its id, use BIT().
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170324163540.31981-3-chris@chris-wilson.co.ukReviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -432,10 +432,10 @@ struct intel_engine_cs {
 	u32 (*get_cmd_length_mask)(u32 cmd_header);
 };
 
-static inline unsigned
+static inline unsigned int
 intel_engine_flag(const struct intel_engine_cs *engine)
 {
-	return 1 << engine->id;
+	return BIT(engine->id);
 }
 
 static inline u32