staging: ath6kl: Convert bypasswmi to bool

Types should match logical uses.
Remove unused extern, make static.

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Vipin Mehta <vipin.mehta@atheros.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>