ubifs: Delete duplicated words + other fixes

Delete repeated words in fs/ubifs/.
{negative, is, of, and, one, it}
where "it it" was changed to "if it".

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
To: linux-fsdevel@vger.kernel.org
Cc: Richard Weinberger <richard@nod.at>
Cc: linux-mtd@lists.infradead.org
Signed-off-by: Richard Weinberger <richard@nod.at>