Fix SAI2A and SAI2B pin muxings for AV96 board on STM32MP15.
Change sai2a-4 & sai2a-5 to sai2a-2 & sai2a-2.
Change sai2a-4 & sai2a-sleep-5 to sai2b-2 & sai2b-sleep-2
Fixes: dcf185ca8175 ("ARM: dts: stm32: Add alternate pinmux for SAI2 pins on stm32mp15")
Signed-off-by: Olivier Moysan <olivier.moysan@xxxxxxxxxxx>