yaffs2: Adjust the timer callback and init functions

The timer callback argument type has been changed by commit 354b46b1
("timer: Switch callback prototype to take struct timer_list *
argument") and init_timer_on_stack() is also removed by commit
9c6c273a ("timer: Remove init_timer_on_stack() in favor of
timer_setup_on_stack()"). Adjust the codes in yaffs2 according to
these changes.

Signed-off-by: Kevin Hao <kexin.hao@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>