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

[ Upstream commit 2e57cefc ]

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: 8492bd91 ("serial: sc16is7xx: fix bug in sc16is7xx_set_baud() when using prescaler")
Signed-off-by: Sasha Levin <sashal@kernel.org>