Replace sai2a-2 node name by sai2a-sleep-2, to avoid name
duplication.

Fixes: 1a9a9d22 ("ARM: dts: stm32: fix AV96 board SAI2 pin muxing on stm32mp15")
Signed-off-by: NOlivier Moysan <olivier.moysan@foss.st.com>
Signed-off-by: NAlexandre Torgue <alexandre.torgue@foss.st.com>