package.bbclass: do_split_packages should always return something.

package.bbclass: do_split_packages should always return something.

So far, when do_split_packages is passed a non-existing folder, it will return nothing.
While building Mesa with PACKAGECONFIG="egl gles" for qemux86, do_package threw a nice exception on a line reading "pkgs += do_split_packages":
"Exception: TypeError: 'NoneType' object is not iterable"
I think a function should always return something, and in this specific case, returning an empty list should be right.
This patch simply fixes the return statement to do just that.

(From OE-Core rev: 39737e00e85bd4a6053f63f0c959fd424aa009be)

Signed-off-by: Josua Mayer <josua.mayer97@gmail.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>