qt5serialbus: install examples to target

When BR2_PACKAGE_QT5BASE_EXAMPLES is set, the examples for this module
are installed in the staging directory but they are not shipped to the
target.

This commit copies the examples `serialbus' from the staging directory
to the target.

Signed-off-by: Gaël PORTAY <gael.portay@savoirfairelinux.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>