b43: fall back gracefully to PIO mode after fatal DMA errors

This makes the b43 driver just automatically fall back to PIO mode when
DMA doesn't work.

The driver already told the user to do it, so rather than have the user
reload the module with a new flag, just make the driver do it
automatically. We keep the message as an indication that something is
wrong, but now just automatically fall back to the hopefully working PIO
case.

(Some post-2.6.33 merge fixups by Larry Finger <Larry.Finger@lwfinger.net>
and yours truly... -- JWL)

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>