kernel-yocto: fix defconfig detection in find_sccs()

kernel-yocto: fix defconfig detection in find_sccs()

The current code would cause a file like "config.bin" to added to the
config sources list. I am sure the intention was to add any files with
defconfig in its name and not the other way around.

Signed-off-by: Gavin Li <gavinli@thegavinli.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>