tools/cppcheck_wrapper.py: fix version string

The warning message displayed when using a different
version of cppcheck was formatted incorrectly. The
correct number of formatting brackets have been
added to resolve this.

Signed-off-by: Brett Warren <brett.warren@arm.com>
Change-Id: Id5d2b946a431d23c0d8efd6e4e71e1f685e88ce7