ARM: dts: stm32: Shorten the AV96 HDMI sound card name

Fix the following error in kernel log due to too long sound card name:
"
asoc-audio-graph-card sound: ASoC: driver name too long 'STM32MP1-AV96-HDMI' -> 'STM32MP1-AV96-H'
"

Fixes: e027da34

 ("ARM: dts: stm32: Add bindings for audio on AV96")
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>