serial: sc16is7xx: replace hardcoded divisor value with BIT() macro

[ Upstream commit 2e57cefc4477659527f7adab1f87cdbf60ef1ae6 ]

To better show why the limit is what it is, since we have only 16 bits for
the divisor.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://lore.kernel.org/r/20231221231823.2327894-13-hugo@hugovil.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: 8492bd91aa05 ("serial: sc16is7xx: fix bug in sc16is7xx_set_baud() when using prescaler")
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/tty/serial/sc16is7xx.c

@@ -497,7 +497,7 @@ static int sc16is7xx_set_baud(struct uart_port *port, int baud)
 	u8 prescaler = 0;
 	unsigned long clk = port->uartclk, div = clk / 16 / baud;
 
-	if (div > 0xffff) {
+	if (div >= BIT(16)) {
 		prescaler = SC16IS7XX_MCR_CLKSEL_BIT;
 		div /= 4;
 	}