ath9k_hw: disabled PAPRD for AR9003

AR9003's PAPRD was enabled prematurely, and is causing some
large discrepancies on throughput and network connectivity.
For example downlink (RX) throughput against an AR9280 AP
can vary widlely from 43-73 Mbit/s while disabling this
gets AR9382 (2x2) up to around 93 Mbit/s in a 2.4 GHz HT20 setup.

Cc: stable@kernel.org
Cc: Paul Shaw <paul.shaw@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>