stm32-dma2d: fix incorrect x swap for swap_x_y.
stm32-dma2d: fix incorrect x swap for swap_x_y.

AdaCore/Ada_Drivers_Library,Fabien-Chouteau/Ada_Drivers_Library,lambourg/Ada_Drivers_Library,simonjwright/Ada_Drivers_Library,ellamosi/Ada_BMP_Library,Fabien-Chouteau/Ada_Drivers_Library,simonjwright/Ada_Drivers_Library,AdaCore/Ada_Drivers_Library