dts: bindings: mmc stm32 sdmmc has a mandatory disk-name

This PR makes the property disk-name required
for the st,stm32-sdmmc compatible

Signed-off-by: Francois Ramu <francois.ramu@st.com>

dts/bindings/mmc/st,stm32-sdmmc.yaml

@@ -7,6 +7,7 @@ include: [mmc.yaml, pinctrl-device.yaml, reset-device.yaml]
 properties:
   disk-name:
     type: string
+    required: true
     description: |
       Disk name.