jfs: delete duplicated words + other fixes

Delete repeated words in fs/jfs/.
{for, allocation, if, the}
Insert "is" in one place to correct the grammar.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
To: linux-fsdevel@vger.kernel.org
Cc: jfs-discussion@lists.sourceforge.net