f2fs: fix to cover f2fs_inline_data_fiemap with inode_lock

This patch fix to cover f2fs_inline_data_fiemap with inode_lock in order
to make that interface avoiding race with mapping change.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>