ARM: dts: stm32: stm32mp151c-plyaqm: Use correct dai-format property

ARM: dts: stm32: stm32mp151c-plyaqm: Use correct dai-format property

The stm32-i2s binding inherits from the standard audio-graph-port
schema for its 'port' subnode, audio-graph-port requires the use
of the 'dai-format' property. The stm32mp151c-plyaqm dts file was
using the non-standard name 'format'.

Correct the property name to 'dai-format' to fix the dtbs_check
validation error.

Fixes: 9365fa46be358 ("ARM: dts: stm32: Add Plymovent AQM devicetree")
Signed-off-by: Jihed Chaibi <jihed.chaibi.dev@gmail.com>
Link: https://lore.kernel.org/r/20250830225115.303663-1-jihed.chaibi.dev@gmail.com
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>