ARM: dts: microchip: sam9x7: Add clock name property

Add clock-output-names to the xtal nodes, so the driver can correctly
register the main and slow xtal.

This fixes the issue of the SoC clock driver not being able to find
the main xtal and slow xtal correctly causing a bad clock tree.

Fixes: 41af45af8bc3 ("ARM: dts: at91: sam9x7: add device tree for SoC")
Signed-off-by: Ryan Wanner <[e-mail]>
Link: https://lore.kernel.org/r/036[e-mail]
Signed-off-by: Claudiu Beznea <[e-mail]>

arch/arm/boot/dts/microchip/sam9x7.dtsi

···
 	clocks {
 		slow_xtal: clock-slowxtal {
 			compatible = "fixed-clock";
+			clock-output-names = "slow_xtal";
 			#clock-cells = <0>;
 		};
 
 		main_xtal: clock-mainxtal {
 			compatible = "fixed-clock";
+			clock-output-names = "main_xtal";
 			#clock-cells = <0>;
 		};
 	};