ath9k_hw: Fix Rx DMA stuck for AR9003 chips

During the endurance testing, rx frames are not getting DMAd from
MAC whereas pcu rx frame counters are getting updated properly.
As per systems team input updated the initval to fix rx dma stuck
issue.

Cc: stable@kernel.org
Signed-off-by: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>