When read BBP registers, avoid writing to BBPCSR until it is no longer busy.

When read BBP registers, avoid writing to BBPCSR until it is no longer busy.
After this bug fixing, TX/RX antenna setup can be safely put after BBP
initialization, which is a correct place for it, since BBP initialization
will overwrite RX antenna BBP register with default value.  Before this bug
fixing, putting TX/RX antenna setup after BBP initailization always results
in strange TX/RX problems, which I experienced when I fiddled with my ASUS
WL-107G; and some OpenBSD folks had this problems too, before Damien reverted
related changes in OpenBSD.

2526 RF does not require special I/Q flipping during TX/RX antenna setup.

Obtained-from: Ralink RT2500 Linux driver