hwmon: (dell-smm) Avoid unnecessary SMM calls during init

hwmon: (dell-smm) Avoid unnecessary SMM calls during init

When the driver tries to detect the fan multiplier during
module initialisation, it issues one SMM call for each fan.
Those SMM calls are however redundant and also try to query
fans which may not be present.
Fix that by detecting the fan multiplier during hwmon
initialisation when no extra SMM calls are needed.
Also dont assume the last nominal speed entry to be the
biggest and instead check all entries.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20220426213154.724708-2-W_Armin@gmx.de
Signed-off-by: Guenter Roeck <linux@roeck-us.net>