logging: Fix _LOG_LEVEL_RESOLVE macro for LOG_LEVEL case

Z_LOG_EVAL returns 1 for non-zero log level so if LOG_LEVEL was 0
with intention to disable logs in the current module Z_LOG_EVAL was
jumping to the second option and was applying default logging level.
Since LOG_LEVEL set to 0 should also lead to evaluation of LOG_LEVEL
COND_CODE_0 is added.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>