ARM: dts: at91: sama5d2/trivial: fix letter case for etm hex address

Fix the etm node hex address to lower case for matching regexp
specification and removing the additional warning that looks like:

arch/arm/boot/dts/at91-sama5d2_ptc_ek.dt.yaml: /: 'etm@73C000' does not
match any of the regexes: '@(0|[1-9a-f][0-9a-f]*)$', '^[^@]+$',
'pinctrl-[0-9]+'
Reported-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm/boot/dts/sama5d2.dtsi

@@ -56,9 +56,9 @@ etb_in: endpoint {
 		};
 	};
 
-	etm@73C000 {
+	etm@73c000 {
 		compatible = "arm,coresight-etm3x", "arm,primecell";
-		reg = <0x73C000 0x1000>;
+		reg = <0x73c000 0x1000>;
 
 		clocks = <&pmc PMC_TYPE_CORE PMC_MCK>;
 		clock-names = "apb_pclk";