spi: dw-mid: fix FIFO size

The FIFO size is 40 accordingly to the specifications, but this means 0x40,
i.e. 64 bytes. This patch fixes the typo and enables FIFO size autodetection
for Intel MID devices.

Fixes: 7063c0d9

 (spi/dw_spi: add DMA support)
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org