spi: pxa2xx: Allow 64-bit DMA

Currently the 32-bit device address only is supported for DMA. However,
starting from Intel Sunrisepoint PCH the DMA address of the device FIFO
can be 64-bit.

Change the respective variable to be compatible with DMA engine
expectations, i.e. to phys_addr_t.

Fixes: 34cadd9c ("spi: pxa2xx: Add support for Intel Sunrisepoint")
Cc: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>