f2fs: reuse core function in f2fs_readdir for inline_dentry

This patch introduces a core function, f2fs_fill_dentries, to remove
redundant code in f2fs_readdir and f2fs_read_inline_dir.

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

diff --cc fs/f2fs/dir.c
Simple merge

diff --cc fs/f2fs/f2fs.h
Simple merge

diff --cc fs/f2fs/inline.c
Simple merge