ath5k: fixing retries in ath5k_hw_setup_4word_tx_desc

The rate control algorithm, default is Minstrel for ath5k, determines
the number of retries to use for each rate.  However, there exists in
ath5k_hw_setup_4word_tx_desc (which is called for AR5212 like devices)
a set number of retries defined by AR5K_TUNE_HWTXTRIES.  The set
number of tries is added to the tx_tries0 variable setup by the rate
control algorithm.  This changes the number of retries the rate
control algorithm considers necessary.  By removing the
AR5K_TUNE_HWTXTRIES from the retry calculation the rate control
algorithm is given control over the number of retries.

Signed-off-by: Andrew Blaich <ablaich@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>