Make /proc/modules use seq_list_xxx helpers

Here there is not need even in .show callback altering.  The original code
passes list_head in *v.

Signed-off-by: Pavel Emelianov <xemul@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>