libcamera: Always check return value of MediaDevice::acquire()

In preparation for adding more responsibility to MediaDevice::acquire()
remove unneeded calls to acquire() and release(), and make sure all
needed calls to acquire() are checked and acted on.

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

test/v4l2_device/v4l2_device_test.cpp

@@ -46,8 +46,6 @@ int V4L2DeviceTest::init()
 	if (!media_)
 		return TestSkip;
 
-	media_->acquire();
-
 	MediaEntity *entity = media_->getEntityByName("vivid-000-vid-cap");
 	if (!entity)
 		return TestSkip;
@@ -61,8 +59,6 @@ int V4L2DeviceTest::init()
 
 void V4L2DeviceTest::cleanup()
 {
-	media_->release();
-
 	capture_->streamOff();
 	capture_->releaseBuffers();
 	capture_->close();