ath9k_htc: Add a module parameter to disable blink

Add an option "blink" to enable or disable the LED blink. The default
value is set to 1 so that existing users would not experience any
unexpected changes.

Signed-off-by: Hong Xu <hong@topbug.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>