iio: dac: ltc2664: Fix off by one in ltc2664_channel_config()

This comparison should be >= ARRAY_SIZE() instead of >.  The "mspan"
variable is later used as an array index into ltc2664_mspan_lut[] so
this is an off by one bug.

Fixes: 4cc2fc44 ("iio: dac: ltc2664: Add driver for LTC2664 and LTC2672")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://patch.msgid.link/5727ab54-6280-466e-b107-1b6006e5ab29@stanley.mountain


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>