UBIFS: rename dbg_check_dir_size function

Since this function is not only about size checking, rename it to
'dbg_check_dir()'.

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

diff --cc fs/ubifs/debug.c
Simple merge

diff --cc fs/ubifs/debug.h
Simple merge

diff --cc fs/ubifs/super.c
Simple merge