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/dev-replace.c b/fs/btrfs/dev-replace.c
index 26bcb48..0584b6c 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -441,7 +441,7 @@
 }
 
 /*
- * blocked until all flighting bios are finished.
+ * blocked until all in-flight bios operations are finished.
  */
 static void btrfs_rm_dev_replace_blocked(struct btrfs_fs_info *fs_info)
 {