iio: ltc2497: Fix reading conversion results

iio: ltc2497: Fix reading conversion results

After the result of the previous conversion is read the chip
automatically starts a new conversion and doesn't accept new i2c
transfers until this conversion is completed which makes the function
return failure.

So add an early return iff the programming of the new address isn't
needed. Note this will not fix the problem in general, but all cases
that are currently used. Once this changes we get the failure back, but
this can be addressed when the need arises.

Fixes: 69548b7c2c4f ("iio: adc: ltc2497: split protocol independent part in a separate module ")
Reported-by: Meng Li <Meng.Li@windriver.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Tested-by: Denys Zagorui <dzagorui@cisco.com>
Cc: <Stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20220815091647.1523532-1-dzagorui@cisco.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>