ARM: dts: Fix SPI node for Arria10

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

Cc: stable@vger.kernel.org
Fixes: f2d6f8f8 ("ARM: dts: socfpga: Add SPI Master1 for Arria10 SR chip")
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>