Cleanup error.h __lttng_print() used for message printing

The loglevels have never really been a mask, and it is useless to try to
use them as masks, because the compiler statically knows the value of
the loglevel requested, and can therefore optimise away all the logic.

This takes care of Coverity warning about mixed bitwise and boolean
logic, which was technically correct, but more complex than needed.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>