USB: serial: f81232: fix division by zero on line-speed change

stable inclusion
from stable-v5.10.161
commit 5b75a004167422f1f4a8af767bd4239e53b3348c
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7P7OH

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5b75a004167422f1f4a8af767bd4239e53b3348c



--------------------------------

commit a08ca6eb upstream.

The driver leaves the line speed unchanged in case a requested speed is
not supported. Make sure to handle the case where the current speed is
B0 (hangup) without dividing by zero when determining the clock source.

Fixes: 268ddb5e ("USB: serial: f81232: add high baud rate support")
Cc: stable@vger.kernel.org      # 5.2
Cc: Ji-Ze Hong (Peter Hong) <hpeter@gmail.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>