tty: serial: fsl_lpuart: adjust buffer length to the intended size

Based on the fls function definition provided below, we should not
subtract 1 to obtain the correct buffer length:

fls(0) = 0, fls(1) = 1, fls(0x80000000) = 32.

Fixes: 5887ad4 ("tty: serial: fsl_lpuart: Use cyclic DMA for Rx")
Signed-off-by: Shenwei Wang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Shenwei Wang

drivers/tty/serial/fsl_lpuart.c

@@ -1296,7 +1296,7 @@ static inline int lpuart_start_rx_dma(struct lpuart_port *sport)
 	 * 10ms at any baud rate.
 	 */
 	sport->rx_dma_rng_buf_len = (DMA_RX_TIMEOUT * baud /  bits / 1000) * 2;
-	sport->rx_dma_rng_buf_len = (1 << (fls(sport->rx_dma_rng_buf_len) - 1));
+	sport->rx_dma_rng_buf_len = (1 << fls(sport->rx_dma_rng_buf_len));
 	if (sport->rx_dma_rng_buf_len < 16)
 		sport->rx_dma_rng_buf_len = 16;