ext[234]: remove unused argument for ext[234]_find_goal()

The argument chain for ext[234]_find_goal() is not used.  This patch removes
it and fixes comment as well.

Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>