hwmon: qpnp-adc: Change initialization order of adc_tm struct members

During the adc_tm probe, when channels register with the thermal
framework, as part of registration, thermal driver tries to set
trip thresholds using adc_tm function. If initializations in this
change are not done early enough, qpnp_adc_tm_set_trip_temp fails
chip validation and returns error early.

Initialize some adc_tm structure members earlier to avoid errors
during thermal registration.

Change-Id: Ia1d0231403e6289c9b0e43e638677b50709c5182
Signed-off-by: Jishnu Prakash <jprakash@codeaurora.org>