hw/ssi: xilinx_spips: Clean up coding convention issues

hw/ssi: xilinx_spips: Clean up coding convention issues

There are some coding convention warnings in xilinx_spips.c,
as reported by:

  $ ./scripts/checkpatch.pl hw/ssi/xilinx_spips.c

Let's clean them up.

Signed-off-by: Xuzhou Cheng <xuzhou.cheng@windriver.com>
Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 20210303135254.3970-5-bmeng.cn@gmail.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>