examples: zephyr: Fix get_temperature with temp0 DT alias

[cdwilson]

When a temp0 devicetree alias is added to the board overlay, the get_temperature function was looping through all sensor channels, always returning the result of reading the last one, even if it was not a supported channel.

This fixes the function so that it returns after the first successful read from a temperature channel.

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Code Coverage

Type	Coverage
lines	55.6% (1035 of 1862 lines)
functions	57.7% (94 of 163 functions)