mlxsw: core_thermal: Fix fan speed in maximum cooling state

The cooling levels array is supposed to prevent the system fans from
being configured below a 20% duty cycle as otherwise some of them get
stuck at 0 RPM.

Due to an off-by-one error, the last element in the array was not
initialized, causing it to be set to zero, which in turn lead to fans
being configured with a 0% duty cycle in maximum cooling state.

Since commit 332fdf95 ("mlxsw: thermal: Fix out-of-bounds memory
accesses") the contents of the array are static. Therefore, instead of
fixing the initialization of the array, simply remove it and adjust
thermal_cooling_device_ops::set_cur_state() so that the configured duty
cycle is never set below 20%.

Before:

 # cat /sys/class/thermal/thermal_zone0/cdev0/type
 mlxsw_fan
 # echo 10 > /sys/class/thermal/thermal_zone0/cdev0/cur_state
 # cat /sys/class/hwmon/hwmon0/name
 mlxsw
 # cat /sys/class/hwmon/hwmon0/pwm1
 0

After:

 # cat /sys/class/thermal/thermal_zone0/cdev0/type
 mlxsw_fan
 # echo 10 > /sys/class/thermal/thermal_zone0/cdev0/cur_state
 # cat /sys/class/hwmon/hwmon0/name
 mlxsw
 # cat /sys/class/hwmon/hwmon0/pwm1
 255

This bug was uncovered when the thermal subsystem repeatedly tried to
configure the cooling devices to their maximum state due to another
issue [1]. This resulted in the fans being stuck at 0 RPM, which
eventually lead to the system undergoing thermal shutdown.

[1] https://lore.kernel.org/netdev/ZA3CFNhU4AbtsP4G@shredder/

Fixes: a421ce08

 ("mlxsw: core: Extend cooling device with cooling levels")
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Vadim Pasternak <vadimp@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>