spi: altera: Use bits_per_word_mask

This driver does not work for bits_per_word greater than 16.
Set bits_per_word_mask so spi core will reject transfers that attempt to use
an unsupported bits_per_word value.

Signed-off-by: Axel Lin <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-altera.c

···
 	master->bus_num = pdev->id;
 	master->num_chipselect = 16;
 	master->mode_bits = SPI_CS_HIGH;
+	master->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 16);
 
 	hw = spi_master_get_devdata(master);
 	platform_set_drvdata(pdev, hw);