Correct explanations of "find_next" bit routines.

Correct the obvious "copy and paste" errors explaining some of the
"find_next" routines.

Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Adrian Bunk <bunk@kernel.org>