ARM: dts: at91: update alternate function of signal PD20

The alternate function of PD20 is 4 as per the datasheet of
sama7g5 and not 5 as defined earlier.

Signed-off-by: Hari Prasath <Hari.PrasathGE@microchip.com>
Fixes: 7540629e ("ARM: dts: at91: add sama7g5 SoC DT and sama7g5-ek")
Cc: <stable@vger.kernel.org> # v5.15+
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20211208063553.19807-1-Hari.PrasathGE@microchip.com