ath9k: fix the return value of ath_stoprecv

The patch 'ath9k_hw: fix stopping rx DMA during resets' added code to detect
a condition where rx DMA was stopped, but the MAC failed to enter the idle
state. This condition requires a hardware reset, however the return value
of ath_stoprecv was 'true' in that case, which allowed it to skip the reset
when issuing a fast channel change.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Reported-by: Paul Stewart <pstew@google.com>
Cc: stable@kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>