recipes, classes: Avoid adding extra whitespace to PACKAGESPLITFUNCS

This is a follow-up to commit 846ff494 to remove the extra whitespace
that is no longer needed after converting :append and :prepend to += and
=+.

Signed-off-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>