spi: Use BITS_TO_BYTES()

BITS_TO_BYTES() is the existing macro which takes care about full
bytes that may fully hold the given amount of bits. Use it.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230714091748.89681-4-andriy.shevchenko@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi.c

@@ -3877,11 +3877,9 @@ static int __spi_validate(struct spi_device *spi, struct spi_message *message)
 	 */
 	if ((spi->mode & SPI_CS_WORD) && (!(ctlr->mode_bits & SPI_CS_WORD) ||
 					  spi_get_csgpiod(spi, 0))) {
-		size_t maxsize;
+		size_t maxsize = BITS_TO_BYTES(spi->bits_per_word);
 		int ret;
 
-		maxsize = (spi->bits_per_word + 7) / 8;
-
 		/* spi_split_transfers_maxsize() requires message->spi */
 		message->spi = spi;