spi: struct device - replace bus_id with dev_name(), dev_set_name()

Cc: dbrownell@users.sourceforge.net
Cc: spi-devel-general@lists.sourceforge.net
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>