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-thin.c b/drivers/md/dm-thin.c
index 9dec2f8..9736621 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -3041,7 +3041,7 @@ static int parse_pool_features(struct dm_arg_set *as, struct pool_features *pf,
 	unsigned argc;
 	const char *arg_name;
 
-	static struct dm_arg _args[] = {
+	static const struct dm_arg _args[] = {
 		{0, 4, "Invalid number of pool feature arguments"},
 	};