arm64: dts: stratix10: Fix SPI nodes for Stratix10

Remove the unused bus-num node and change num-chipselect
to num-cs to match SPI bindings.

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>
Signed-off-by: Olof Johansson <olof@lixom.net>