btrfs: fix string and comment grammatical issues and typos

Signed-off-by: Nicholas D Steeves <nsteeves@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/ordered-data.h b/fs/btrfs/ordered-data.h
index 23c9605..ae068bb 100644
--- a/fs/btrfs/ordered-data.h
+++ b/fs/btrfs/ordered-data.h
@@ -58,7 +58,7 @@
 
 #define BTRFS_ORDERED_COMPRESSED 3 /* writing a zlib compressed extent */
 
-#define BTRFS_ORDERED_PREALLOC 4 /* set when writing to prealloced extent */
+#define BTRFS_ORDERED_PREALLOC 4 /* set when writing to preallocated extent */
 
 #define BTRFS_ORDERED_DIRECT 5 /* set when we're doing DIO with this extent */