Registers used for indirect BBP and RF registers access are
respectively BBPCSR and RFCSR, also make it clear that all CSR
registers access goes through rt2x00pci_register_[read,write]()
methods.
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com> Acked-by: Ivo van Doorn <IvDoorn@gmail.com> Acked-by: Gertjan van Wingerde <gwingerde@gmail.com> Signed-off-by: John W. Linville <linville@tuxdriver.com>