tracing: Fix recordmcount.pl to handle sections with only weak functions

Roland Dreier found that a section that contained only a weak
function in one of the staging drivers and this caused
recordmcount.pl to spit out a warning and fail.

Although it is strange that a driver would have a weak function, and
this function only be used in one place, it should not be something
to make recordmcount.pl fail.

This patch fixes the issue in a simple manner: if only weak
functions exist in a section, then that section will not be
recorded.

Reported-by: Roland Dreier <rdreier@cisco.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>