thermal: qcom: Fix comparison with uninitialized variable channels_available

Currently the check of chip->channels[i].channel is against an the
uninitialized variable channels_available.  I believe the variable
channels_available needs to be fetched first by the call to adc_tm5_read
before the channels check. Fix the issue swapping the order of the
channels check loop with the call to adc_tm5_read.

Addresses-Coverity: ("Uninitialized scalar variable")
Fixes: ca66dca5 ("thermal: qcom: add support for adc-tm5 PMIC thermal monitor")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210216151626.162996-1-colin.king@canonical.com