dm: constify argument arrays

The arrays of 'struct dm_arg' are never modified by the device-mapper
core, so constify them so that they are placed in .rodata.

(Exception: the args array in dm-raid cannot be constified because it is
allocated on the stack and modified.)

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index c5ea03f..b0a5503a 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -2306,7 +2306,7 @@ static void init_features(struct cache_features *cf)
 static int parse_features(struct cache_args *ca, struct dm_arg_set *as,
 			  char **error)
 {
-	static struct dm_arg _args[] = {
+	static const struct dm_arg _args[] = {
 		{0, 2, "Invalid number of cache feature arguments"},
 	};
 
@@ -2348,7 +2348,7 @@ static int parse_features(struct cache_args *ca, struct dm_arg_set *as,
 static int parse_policy(struct cache_args *ca, struct dm_arg_set *as,
 			char **error)
 {
-	static struct dm_arg _args[] = {
+	static const struct dm_arg _args[] = {
 		{0, 1024, "Invalid number of policy arguments"},
 	};