ath6kl: consolidate WoW pattern length

Since WOW_MASK_SIZE and WOW_PATTERN_SIZE have the same value, are
logically equivalent, and part of the WMI API so therefore unlikely to
change, consolidate these into WOW_PATTERN_SIZE.

Reported-by Kalle Valo <kvalo@qualcomm.com>
Signed-off-by: Thomas Pedersen <c_tpeder@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>