log: don't build the trace buffer when log is not ready

Update _log function to drop any traces when log is yet initialized:
vsnprintf is no more executed in this case.

This patch allows to reduce the cost for the dropped early debug trace.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
1 file changed