spi: Fix checkpatch issue

Fix the following checkpatch error and warnings.

  ERROR: space required after that ',' (ctx:VxV)
  WARNING: quoted string split across lines
  WARNING: max() should probably be max_t(int, nb, master->num_chipselect)
  WARNING: sizeof *spi should be sizeof(*spi)
  WARNING: sizeof *master should be sizeof(*master)
  WARNING: sizeof x should be sizeof(x)

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Mark Brown <broonie@linaro.org>