There is no need to check FILES in each loop iteration, we can just check it once
at the start when we read the variable.
(From OE-Core rev: 1bcc5cba12cbb1b846b433719d1b0820f5a97105)
(From OE-Core rev: 40542f7a46bfb8431e31eca9af06adb4b343d810)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>