f2fs: support fault injection for dquot_initialize()

This patch adds a new function f2fs_dquot_initialize() to wrap
dquot_initialize(), and it supports to inject fault into
f2fs_dquot_initialize() to simulate inner failure occurs in
dquot_initialize().

Usage:
a) echo 65536 > /sys/fs/f2fs/<dev>/inject_type or
b) mount -o fault_type=65536 <dev> <mountpoint>

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>