fix memory leak when /proc/yaffs is read

fix memory leak when /proc/yaffs is read

Thanks to Jisheng Zhang <Jisheng.Zhang@synaptics.com> for supplying this patch

There is a kernel memory leak observed when the proc file /proc/yaffs
is read. This reason is that in yaffs_proc_open, single_open is called
and the respective release function is not called during release.

Fix with correct release function - single_release().

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>