arm64: dts: stratix10: Correct System Manager register size

Correct the register size of the System Manager node.

Cc: stable@vger.kernel.org
Fixes: 78cd6a9d

 ("arm64: dts: Add base stratix 10 dtsi")
Signed-off-by: Thor Thayer <thor.thayer@linux.intel.com>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>