logging: Fix fail when log locally disabled

When log is locally disabled then structures associated with the module
are not created. Logger API macros were evaluating those structues even
when log was disabled for given module. That resulted in compilation
error. Macros has been improved to not touch those structures when
log is disabled for given module.

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