ath9k and ath9k_htc: rename variable "led_blink"

ath9k and ath9k_htc use the variable name "led_blink" to indicate
whether the module parameter "blink" is on. This name is easy to
conflict with other variables, and has caused a compiler error found
by kbuild test bot. The compiler error is as following:

drivers/net/wireless/ath/ath9k/ath9k_htc.o:(.data+0x47c): multiple definition of `led_blink'
drivers/net/wireless/ath/ath9k/ath9k.o:(.bss+0x20): first defined here

Fixes: 3a939a67 ("ath9k_htc: Add a module parameter to disable blink")
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Hong Xu <hong@topbug.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>