btrfs: rename variable holding per-inode compression type

This is preparatory for separating inode compression requested by defrag
and set via properties. This will fix a usability bug when defrag will
reset compression type to NONE. If the file has compression set via
property, it will not apply anymore (until next mount or reset through
command line).

We're going to fix that by adding another variable just for the defrag
call and won't touch the property. The defrag will have higher priority
when deciding whether to compress the data.

Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/btrfs_inode.h

@@ -179,9 +179,9 @@ struct btrfs_inode {
 	unsigned reserved_extents;
 
 	/*
-	 * always compress this one file
+	 * Cached values of inode properties
 	 */
-	unsigned force_compress;
+	unsigned prop_compress;		/* per-file compression algorithm */
 
 	struct btrfs_delayed_node *delayed_node;