arm: dts: k3-am64-ddr fix typo causing DDR4 register corruption

The entry for DDRSS_PI_321_DATA was accidentally repeated leading to the
last few PI registers being incorrectly programmed.

Fix this.

Reported-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Anand Gadiyar <gadiyar@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>