rt2x00: Use pci_is_pcie()

Use function pci_is_pcie() instead of accessing struct member directly.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>