Replace unnecessary if with else statement.

This fixes the following (false) compile warning reported with some combinations
of C compiler version and configuration.

drivers/hwmon/ntc_thermistor.c: In function 'ntc_show_temp':
drivers/hwmon/ntc_thermistor.c:225: warning: 'low' may be used uninitialized in
this function
drivers/hwmon/ntc_thermistor.c:225: note: 'low' was declared here
drivers/hwmon/ntc_thermistor.c:225: warning: 'high' may be used uninitialized in
this function
drivers/hwmon/ntc_thermistor.c:225: note: 'high' was declared here
drivers/hwmon/ntc_thermistor.c:294: warning: 'temp' may be used uninitialized in
this function

Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Acked-by: Jean Delvare <khali@linux-fr.org>