spi_nxp_lpspi: Fix TX word formation for multibyte

For multi-byte word, there is clearly a bug in that the same byte is
written to each spot in the word instead of writing all the bytes
properly.

Signed-off-by: Declan Snyder <[email protected]>
(cherry picked from commit 97e29a9)

Author: decsny

drivers/spi/spi_nxp_lpspi/spi_nxp_lpspi.c

@@ -115,7 +115,7 @@ static inline uint32_t lpspi_next_tx_word(const struct device *dev, int offset)
 	uint32_t next_word = 0;
 
 	for (uint8_t i = 0; i < num_bytes; i++) {
-		next_word |= *byte << (BITS_PER_BYTE * i);
+		next_word |= byte[i] << (BITS_PER_BYTE * i);
 	}
 
 	return next_word;