WDEV, ath5k, don't return int from bool function

sparse sees int -> bool cast as an error:
hw.c:3754:10: warning: cast truncates bits from constant value (ffffffea becomes 0)
Fix it by converting the rettype to int and check appropriately.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Nick Kossifidis <mickflemm@gmail.com>
Cc: Luis R. Rodriguez <mcgrof@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>