ath9k: Reduce PLL Settle time and eliminate redundant PLL calls.

Reduce PLL Settle time and eliminate redundant PLL calls. Also reduce
the LoadNF timeout from 10 msec to 250usec as the 10 msec timeout was
hit with AR9285 in some cases.

Signed-off-by: Senthil Balasubramanian <senthilkumar@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>