libcamera: Drop explicit construction of std::queue

Now that libcamera is using C++17 and requires gcc 7 or newer, we can
use the implicit std::queue constructor. Simplify the code accordingly.

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

src/libcamera/pipeline/ipu3/cio2.cpp

@@ -300,9 +300,7 @@ void CIO2Device::tryReturnBuffer(FrameBuffer *buffer)
 
 void CIO2Device::freeBuffers()
 {
-	/* The default std::queue constructor is explicit with gcc 5 and 6. */
-	availableBuffers_ = std::queue<FrameBuffer *>{};
-
+	availableBuffers_ = {};
 	buffers_.clear();
 
 	if (output_->releaseBuffers())

src/libcamera/pipeline/raspberrypi/raspberrypi.cpp

@@ -848,9 +848,8 @@ void PipelineHandlerRPi::stop(Camera *camera)
 
 	/* This also stops the streams. */
 	data->clearIncompleteRequests();
-	/* The default std::queue constructor is explicit with gcc 5 and 6. */
-	data->bayerQueue_ = std::queue<FrameBuffer *>{};
-	data->embeddedQueue_ = std::queue<FrameBuffer *>{};
+	data->bayerQueue_ = {};
+	data->embeddedQueue_ = {};
 
 	/* Stop the IPA. */
 	data->ipa_->stop();