libcamera: Replace usage of lroundf() with std::lround()

As explained in the coding style document, usage of std::lround() is
preferred over lroundf() as it picks the correct function based on
the argument type. Replace calls to lroundf() with std::lround() through
libcamera.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>

Documentation/guides/pipeline-handler.rst

@@ -1350,7 +1350,7 @@ before being set.
                         continue;
                  }
 
-                 int32_t value = lroundf(it.second.get<float>() * 128 + offset);
+                 int32_t value = std::lround(it.second.get<float>() * 128 + offset);
                  controls.set(cid, std::clamp(value, 0, 255));
           }
 
@@ -1414,7 +1414,7 @@ value translation operations:
 
 .. code-block:: cpp
 
-   #include <math.h>
+   #include <cmath>
 
 Frame completion and event handling
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~