hwmon: (npcm-750-pwm-fan) Change initial pwm target to 255

[ Upstream commit f21c8e753b1dcb8f9e5b096db1f7f4e6fdfa7258 ]

Change initial PWM target to 255 to prevent overheating, for example
when BMC hangs in userspace or when userspace fan control application is
not implemented yet.

Signed-off-by: Kun Yi <kunyi@google.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>