spi: dw-pci: remove unused pdev member from struct dw_spi_pci

The pdev member is not used anywhere, thus remove it. Moreover struct
dw_spi_pci becomes an equivalent of struct dw_spi and therefore remove entire
struct dw_spi_pci.

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