libcamera: V4L2BufferCache: Use the entry reference

Instead of looking up the index in the storage vector use the reference
to it created at the beginning of the loop.

Signed-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/libcamera/v4l2_videodevice.cpp

@@ -216,7 +216,7 @@ int V4L2BufferCache::get(const FrameBuffer &buffer)
 			use = index;
 
 		/* Try to find a cache hit by comparing the planes. */
-		if (cache_[index] == buffer) {
+		if (entry == buffer) {
 			hit = true;
 			use = index;
 			break;