Net: wireless: ath: fix macros coding style issue in hw.c

This is a patch to the ath/hw.c file that fixes up a warning about
macros found by the checkpatch.pl tool, that said that complex values
should be enclosed in parenthesis.

Signed-off-by: Luis de Bethencourt <luisbg@ubuntu.com>
Acked-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>