ath: constify local structures

For structure types defined in the same file or local header files, find
top-level static structure declarations that have the following
properties:
1. Never reassigned.
2. Address never taken
3. Not passed to a top-level macro call
4. No pointer or array-typed field passed to a function or stored in a
variable.
Declare structures having all of these properties as const.

Done using Coccinelle.
Based on a suggestion by Joe Perches <joe@perches.com>.
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/ath/dfs_pattern_detector.c

@@ -338,7 +338,7 @@ static bool dpd_set_domain(struct dfs_pattern_detector *dpd,
 	return true;
 }
 
-static struct dfs_pattern_detector default_dpd = {
+static const struct dfs_pattern_detector default_dpd = {
 	.exit		= dpd_exit,
 	.set_dfs_domain	= dpd_set_domain,
 	.add_pulse	= dpd_add_pulse,