arm64: dts: freescale: imx8mq-librem5: align operating-points table name with dtschema

Align the name of operating-points node to dtschema to fix warnings like:

  ddrc-opp-table: $nodename:0: 'ddrc-opp-table' does not match '^opp-table(-[a-z0-9]+)?$'
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mq-librem5.dtsi

@@ -225,7 +225,7 @@ &A53_3 {
 &ddrc {
 	operating-points-v2 = <&ddrc_opp_table>;
 
-	ddrc_opp_table: ddrc-opp-table {
+	ddrc_opp_table: opp-table {
 		compatible = "operating-points-v2";
 
 		opp-25M {