rt2x00: fix warning when building rt2800pci with just soc support

Fix compile warning "rt2800pci.c:1248: warning: 'rt2800pci_device_table'
defined but not used" when building rt2800pci with only soc support
(without pci).

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>