libcamera: buffer: Drop private function setRequest()

There is no need to have a private helper function to access a private
data member when a friend statement is needed anyhow. Remove the helper
function to simplify the code and make it clear that a private member of
Buffer is accessed.

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

src/libcamera/buffer.cpp

@@ -290,7 +290,6 @@ Buffer::Buffer(unsigned int index, const Buffer *metadata)
  *
  * \return The Request the Buffer belongs to, or nullptr if the buffer is
  * either completed or not associated with a request
- * \sa Buffer::setRequest()
  */
 
 /**
@@ -318,10 +317,11 @@ void Buffer::cancel()
 }
 
 /**
- * \fn Buffer::setRequest()
- * \brief Set the request this buffer belongs to
+ * \var Buffer::request_
+ * \brief The request this buffer belongs to
  *
- * The intended callers are Request::addBuffer() and Request::completeBuffer().
+ * This member is intended to be set by Request::addBuffer() and
+ * Request::completeBuffer().
  */
 
 /**