UBIFS: improve function-level documentation

Fix various inconsistencies in the documentation associated with various
functions.

In the case of fs/ubifs/lprops.c, the second parameter of
ubifs_get_lp_stats was renamed from st to lst in commit 84abf972ccff
("UBIFS: add re-mount debugging checks")

In the case of fs/ubifs/lpt_commit.c, the excess variables have never
existed in the associated functions since the code was introduced into the
kernel.

The others appear to be straightforward typos.

Issues detected using Coccinelle (http://coccinelle.lip6.fr/)

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Richard Weinberger <richard@nod.at>