cleanup-trace-events.pl: Tighten search for trace event call

The script can get fooled too easily.  For instance, it finds
trace_megasas_io_read_start when looking for trace_megasas_io_read,
and incorrectly concludes that event megasas_io_read is used.

Supply -w to git-grep to tighten the search.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Message-id: 1411476811-24251-2-git-send-email-armbru@redhat.com
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

scripts/cleanup-trace-events.pl

@@ -25,7 +25,7 @@ sub out {
 
 while (<>) {
     if (/^(disable )?([a-z_0-9]+)\(/) {
-        open GREP, '-|', 'git', 'grep', '-l', "trace_$2"
+        open GREP, '-|', 'git', 'grep', '-lw', "trace_$2"
             or die "run git grep: $!";
         my $fname;
         while ($fname = <GREP>) {