hwmon: (ltc2991) re-order conditions to fix off by one bug

hwmon: (ltc2991) re-order conditions to fix off by one bug

LTC2991_T_INT_CH_NR is 4.  The st->temp_en[] array has LTC2991_MAX_CHANNEL
(4) elements.  Thus if "channel" is equal to LTC2991_T_INT_CH_NR then we
have read one element beyond the end of the array.  Flip the conditions
around so that we check if "channel" is valid before using it as an array
index.

Fixes: 2b9ea4262ae9 ("hwmon: Add driver for ltc2991")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/Zoa9Y_UMY4_ROfhF@stanley.mountain
Signed-off-by: Guenter Roeck <linux@roeck-us.net>