logging: move _is_user_context() check down one level

MISRA-C Directive 4.7 says that error information returned from
a function needs to be tested. In the logging macros,
return from _is_user_context() is not needed until logging is
enabled and above minimal logging level. There is a potential
that the return is not being used at all. So move it one level
below as it is surely being used within the if block.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>