generic swap(): ath9k: rename swap() to swap_array()

In preparation for the introduction of a generic swap() macro.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Sujith Manoharan <Sujith.Manoharan@atheros.com>
Cc: Luis R. Rodriguez <lrodriguez@atheros.com>
Cc: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Cc: Senthil Balasubramanian <senthilkumar@atheros.com>
Cc: Jouni Malinen <jouni.malinen@atheros.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>