libcamera: pipeline: virtual: Don't use span iterator as pointer

Pointer to the contiguous data of a container is to be retrieved
using the `data()` member function. Using `begin()` in contexts
that require pointers is not correct as the iterator may be
something entirely different. So use `data()` where applicable.

Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Isaac Scott <isaac.scott@ideasonboard.com>

src/libcamera/pipeline/virtual/image_frame_generator.cpp

@@ -136,8 +136,9 @@ int ImageFrameGenerator::generateFrame(const Size &size, const FrameBuffer *buff
 
 	/* Write the scaledY and scaledUV to the mapped frame buffer */
 	libyuv::NV12Copy(scaledFrameDatas_[frameIndex_].Y.get(), size.width,
-			 scaledFrameDatas_[frameIndex_].UV.get(), size.width, planes[0].begin(),
-			 size.width, planes[1].begin(), size.width,
+			 scaledFrameDatas_[frameIndex_].UV.get(), size.width,
+			 planes[0].data(), size.width,
+			 planes[1].data(), size.width,
 			 size.width, size.height);
 
 	/* Proceed to the next image every 4 frames */

src/libcamera/pipeline/virtual/test_pattern_generator.cpp

@@ -53,8 +53,8 @@ int TestPatternGenerator::generateFrame(const Size &size,
 
 	/* Convert the template_ to the frame buffer */
 	int ret = libyuv::ARGBToNV12(template_.get(), size.width * kARGBSize,
-				     planes[0].begin(), size.width,
-				     planes[1].begin(), size.width,
+				     planes[0].data(), size.width,
+				     planes[1].data(), size.width,
 				     size.width, size.height);
 	if (ret != 0)
 		LOG(Virtual, Error) << "ARGBToNV12() failed with " << ret;