ath9k: Cleanup beacon stuck processing

We never use SC_OP_NO_RESET, it is not configurable at all.
Remove all code that deals with this flag and make beacon
stuck processing simple.

Signed-off-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>