btrfs-progs: check: Cleanup all checkpatch error and warning

btrfs-progs: check: Cleanup all checkpatch error and warning

Since we're moving tons of code, it's a good idea to fix all errors and
warnings from checkpatch.

Note: we don't rely on checkpatch, take its warnings and errors as a
      hint and do not blindly fix anything that gets reported. The code
      follows some style that should be kept and is not in 100% with
      what checkpatch finds. Always apply your common sense and decide
      if the change makes sense or if it is really making the code
      better.

Additional fixes from dsterba:

- %Lu -> %llu
- lowercase first word or messages

Signed-off-by: Qu Wenruo <wqu@suse.com>
[ added note ]
Signed-off-by: David Sterba <dsterba@suse.com>