UBIFS: add a print, fix comments and more minor stuff

This commit adds a reserved pool size print and tweaks the
prints to make them look nicer.

It also fixes and cleans-up some comments.

Additionally, it deletes some blank lines to make the code look
a little nicer.

In other words, nothing essential.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>