hwmon: (lm93) Drop unnecessary compare statement

The following build warning is seen with -Wextra.

lm93.c: In function ‘store_fan_smart_tach’:
lm93.c:1833:2: warning: comparison of unsigned expression >= 0 is always true

Drop the unnecessary comparison.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Jean Delvare <khali@linux-fr.org>