serial: fsl_lpuart: Remove custom frame size calculation

The number of bits can be calculated using tty_get_frame_size(), no
need for the driver to do it on its own. Change bits to unsigned and
baud too since we're touching the declarations line anyway (the
respective core functions are typed unsigned).
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220830084925.5608-4-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/fsl_lpuart.c

@@ -1284,17 +1284,12 @@ static inline int lpuart_start_rx_dma(struct lpuart_port *sport)
 	struct dma_slave_config dma_rx_sconfig = {};
 	struct circ_buf *ring = &sport->rx_ring;
 	int ret, nent;
-	int bits, baud;
 	struct tty_port *port = &sport->port.state->port;
 	struct tty_struct *tty = port->tty;
 	struct ktermios *termios = &tty->termios;
 	struct dma_chan *chan = sport->dma_rx_chan;
-
-	baud = tty_get_baud_rate(tty);
-
-	bits = (termios->c_cflag & CSIZE) == CS7 ? 9 : 10;
-	if (termios->c_cflag & PARENB)
-		bits++;
+	unsigned int bits = tty_get_frame_size(termios->c_cflag);
+	unsigned int baud = tty_get_baud_rate(tty);
 
 	/*
 	 * Calculate length of one DMA buffer size to keep latency below