rockchip: Don't clear the reset status reg

rockchip: Don't clear the reset status reg

reset reason can be used several stages of U-Boot bootloader
like SPL, U-Boot proper based on the requirements.

Clearing the status register end of get_reset_cause will end
up showing the wrong reset cause when it read the second time.
For example, if board resets, SPL reads the reset status as
RST whereas U-Boot proper reads the status as POR.

However, based on the latest testing clearing reset status
won't be required for determine the last reset cause or
following resets.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>