tests: logging: log_api: Use positive CONFIG_LOG_BUFFER_SIZE

When immediate mode is used CONFIG_LOG_BUFFER_SIZE is not defined
in kconfig. For proper compilation it is then defined in the test
file. Use positive value to please coverity which complains about
dead code when it is set to 0. Fixing CID 235961, 235965.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>
1 file changed