traceroute: filter-out patches dir

The $(subdirs) contains all the dirs under the ${B}, and this one:

do_unpack[cleandirs] = "${S}/patches"

will create a "patches" dir, then there will be compile errors, filter
out the patches will fix the problem.

Note: poky doesn't have this problem since it separates the ${S} and
${B}

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Joe MacDonald <joe.macdonald@windriver.com>