spi: dw: Discard IRQ threshold macro

The macro has been unused since a half of FIFO length was defined to be a
marker of the IRQ. Let's remove it definition.
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Link: https://lore.kernel.org/r/20200920112914.26501-2-Sergey.Semin@baikalelectronics.ruSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-dw.h

@@ -92,9 +92,6 @@
 #define SPI_DMA_RDMAE			(1 << 0)
 #define SPI_DMA_TDMAE			(1 << 1)
 
-/* TX RX interrupt level threshold, max can be 256 */
-#define SPI_INT_THRESHOLD		32
-
 enum dw_ssi_type {
 	SSI_MOTO_SPI = 0,
 	SSI_TI_SSP,