py: MappedFrameBuffer: Add 'fb' property

Add 'fb' property to expose the underlying FrameBuffer.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/py/libcamera/utils/MappedFrameBuffer.py

@@ -99,3 +99,7 @@ class MappedFrameBuffer:
             raise RuntimeError('MappedFrameBuffer not mmapped')
 
         return self.__planes
+
+    @property
+    def fb(self):
+        return self.__fb