libcamera: pixel_format: remove duplicated return documentation

The PixelFormat::toString() has two \return statements in its
doxygen documentation.

Remove the redundant one.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/libcamera/pixel_format.cpp

@@ -132,7 +132,6 @@ std::string PixelFormat::toString() const
 
 /**
  * \brief Create a PixelFormat from a string
- * \return Pixel format
  * \return The PixelFormat represented by the \a name if known, or an
  * invalid pixel format otherwise.
  */