kernel.bbclass: check, if directory exists before removing empty module directory

kernel.bbclass: check, if directory exists before removing empty module directory

If the kernel folder does not exist, find will result in an error.
This can occur if the kernel has no modules but, for example, custom modules are created.

Add check before deleting.

Signed-off-by: Heiko Thole <heiko.thole@entwicklung.eq-3.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 7ef767d84d56b25498e45db83bb8f9d9caebeaf9)
Signed-off-by: Steve Sakoman <steve@sakoman.com>