arm64: dts: ti: k3-am64-main: Fix ospi compatible

The TI specific compatible should be followed by the generic
"cdns,qspi-nor" compatible.

Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/20210326130034.15231-4-p.yadav@ti.com