ath9k: Re-enable interrupts after a channel change failure

ath_complete_reset will not be called if ath9k_hw_reset
is unsuccessful, so we need to re-enable intertupts to
balence the previous ath_prepare_reset call.  Also schedule a
reset as a best effort method to recover the chip from
whatever state caused the channel change failure.

Fixes https://bugzilla.kernel.org/show_bug.cgi?id=55771



Signed-off-by: Robert Shade <robert.shade@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>