drivers/net/wireless/ath/ath9k: use ARRAY_SIZE macro in ani.c

Replace (sizeof(ofdm_level_table)/sizeof(ofdm_level_table[0]) with
ARRAY_SIZE(ofdm_level_table), and (sizeof(cck_level_table)/
sizeof(cck_level_table[0]) with ARRAY_SIZE(cck_level_table) in
drivers/net/wireless/ath/ath9k/ani.c

Signed-off-by: Nikitas Angelinas <nikitasangelinas@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>