hwmon: (dell-smm) Rework SMM function debugging

Drop #ifdef DEBUG and use ktime_us_delta()
for improved precision.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Reviewed-by: Pali Rohár <pali@kernel.org>
Link: https://lore.kernel.org/r/20210814190516.26718-1-W_Armin@gmx.de


Signed-off-by: Guenter Roeck <linux@roeck-us.net>