ARM: dts: at91: sama7g5: fix signal name of pin PD8

The signal name of pin PD8 with function D is A22_NANDCLE
as it is defined in the datasheet.

Fixes: 558378a4 ("ARM: mach-at91: add support for new SoC sama7g5")
Signed-off-by: Mihai Sain <mihai.sain@microchip.com>