rockchip: rk3399-puma: preserve leading zeros in serial#

rockchip: rk3399-puma: preserve leading zeros in serial#

Linux preserves leading zeros in /proc/cpuinfo, so we
should as well.

Otherwise we have the situation that
/sys/firmware/devicetree/base/serial-number
and /proc/cpuinfo disagree in Linux.

Signed-off-by: Jakob Unterwurzacher <jakob.unterwurzacher@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>