dt-bindings: rtc: at91: rename rtt bindings file

atmel,at91sam9-rtc is a confusing name for this file as it is documenting
the RTT used as an RTC and not the other regular RTC (atmel,at91rm9200-rtc
and atmel,at91sam9x5-rtc)
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20220308155735.54146-1-alexandre.belloni@bootlin.com

Documentation/devicetree/bindings/rtc/atmel,at91sam9-rtc.yaml → Documentation/devicetree/bindings/rtc/atmel,at91sam9260-rtt.yaml

@@ -2,7 +2,7 @@
 # Copyright (C) 2022 Microchip Technology, Inc. and its subsidiaries
 %YAML 1.2
 ---
-$id: http://devicetree.org/schemas/rtc/atmel,at91sam9-rtc.yaml#
+$id: http://devicetree.org/schemas/rtc/atmel,at91sam9260-rtt.yaml#
 $schema: http://devicetree.org/meta-schemas/core.yaml#
 
 title: Atmel AT91 RTT Device Tree Bindings