rt2x00: Always set BBP_CSR_CFG_BBP_RW_MODE to 1

Latest rt2870 legacy driver also sets BBP_CSR_CFG_BBP_RW_MODE to 1
when reading or writing the EEPROM. This means we can make the
BBP reading and writing completely equal on all platforms.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>