serial: mvebu-uart: correctly calculate minimal possible baudrate

stable inclusion
from stable-5.10.50
commit 347af865b6a20d2f498644f612c0e09d2eeba199
bugzilla: 174522 https://gitee.com/openeuler/kernel/issues/I4DNFY

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=347af865b6a20d2f498644f612c0e09d2eeba199



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[ Upstream commit deeaf963 ]

For default (x16) scheme which is currently used by mvebu-uart.c driver,
maximal divisor of UART base clock is 1023*16. Therefore there is limit for
minimal supported baudrate. This change calculate it correctly and prevents
setting invalid divisor 0 into hardware registers.

Signed-off-by: Pali Rohár <pali@kernel.org>
Fixes: 68a0db1d ("serial: mvebu-uart: add function to change baudrate")
Link: https://lore.kernel.org/r/20210624224909.6350-4-pali@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>