spi: altera: Use DIV_ROUND_UP to calculate hw->bytes_per_word

The Altera SPI hardware can be configured to support data width from 1 to 32
since Quartus II 8.1. To avoid truncation by integer division, use DIV_ROUND_UP
to calculate hw->bytes_per_word.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Thomas Chou <thomas@wytron.com.tw>
Signed-off-by: Mark Brown <broonie@linaro.org>