[PATCH] bcm43xx: Drain TX status before starting IRQs

Drain the Microcode TX-status-FIFO before we enable IRQs.
This is required, because the FIFO may still have entries left
from a previous run. Those would immediately fire after enabling
IRQs and would lead to an oops in the DMA TXstatus handling code.

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>