btrfs: constify static arrays

There are a few statically initialized arrays that can be made const.
The remaining (like file_system_type, sysfs attributes or prop handlers)
do not allow that due to type mismatch when passed to the APIs or
because the structures are modified through other members.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -174,7 +174,7 @@ struct btrfs_ordered_sum;
 /* csum types */
 #define BTRFS_CSUM_TYPE_CRC32	0
 
-static int btrfs_csum_sizes[] = { 4 };
+static const int btrfs_csum_sizes[] = { 4 };
 
 /* four bytes for CRC32 */
 #define BTRFS_EMPTY_DIR_SIZE 0

fs/btrfs/inode.c

@@ -83,7 +83,7 @@ struct kmem_cache *btrfs_path_cachep;
 struct kmem_cache *btrfs_free_space_cachep;
 
 #define S_SHIFT 12
-static unsigned char btrfs_type_by_mode[S_IFMT >> S_SHIFT] = {
+static const unsigned char btrfs_type_by_mode[S_IFMT >> S_SHIFT] = {
 	[S_IFREG >> S_SHIFT]	= BTRFS_FT_REG_FILE,
 	[S_IFDIR >> S_SHIFT]	= BTRFS_FT_DIR,
 	[S_IFCHR >> S_SHIFT]	= BTRFS_FT_CHRDEV,

fs/btrfs/ioctl.c

@@ -5286,7 +5286,7 @@ static int btrfs_ioctl_set_fslabel(struct file *file, void __user *arg)
 static int btrfs_ioctl_get_supported_features(struct file *file,
 					      void __user *arg)
 {
-	static struct btrfs_ioctl_feature_flags features[3] = {
+	static const struct btrfs_ioctl_feature_flags features[3] = {
 		INIT_FEATURE_FLAGS(SUPP),
 		INIT_FEATURE_FLAGS(SAFE_SET),
 		INIT_FEATURE_FLAGS(SAFE_CLEAR)

fs/btrfs/super.c

@@ -309,7 +309,7 @@ enum {
 	Opt_err,
 };
 
-static match_table_t tokens = {
+static const match_table_t tokens = {
 	{Opt_degraded, "degraded"},
 	{Opt_subvol, "subvol=%s"},
 	{Opt_subvolid, "subvolid=%s"},