tracing/fastboot: fix perlcritic warning

Impact: cleanup

Fix the following warning from the perl syntax checking tool perlcritic.
This tool is a lint like tool that checks for perl best practices.

Loop iterator is not lexical at line 113, column 1.
See page 108 of PBP.  (Severity: 5)

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>