reiserfs: use generic_cont_expand_simple

This patch makes reiserfs to use AOP_FLAG_CONT_EXPAND
in order to get rid of the special generic_cont_expand routine

Signed-off-by: Vladimir Saveliev <vs@namesys.com>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>