spi: dw: remove unneeded cr0 member of struct chip_data

Since we recalculate cr0 each time we start a transfer the chip_data->cr0
becomes redundant. Remove it and related pieces.

This is a follow up to commit 0ed36990 (spi: dw: Remove needless if
statements).

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>