UBIFS: fix compilation warnings when compiling with gcc 4.5

When compiling UBIFS with CONFIG_UBIFS_FS_DEBUG not set,
gcc-4.5.2 generates a slew of "warning: statement with no effect"
on references to non-void functions defined as 0.
To avoid these warnings, replace #defines with dummy inline functions.

Artem: massage the patch a bit, also remove the duplicate
       'dbg_check_lprops()' prototype.

Signed-off-by: Maksim Rayskiy <maksim.rayskiy@gmail.com>
Acked-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>