f2fs: fix to skip verifying block address for non-regular inode

f2fs: fix to skip verifying block address for non-regular inode

generic/184 1s ... [failed, exit status 1]- output mismatch
    --- tests/generic/184.out	2015-01-11 16:52:27.643681072 +0800
     QA output created by 184 - silence is golden
    +rm: cannot remove '/mnt/f2fs/null': Bad address
    +mknod: '/mnt/f2fs/null': Bad address
    +chmod: cannot access '/mnt/f2fs/null': Bad address
    +./tests/generic/184: line 36: /mnt/f2fs/null: Bad address
    ...

F2FS-fs (zram0): access invalid blkaddr:259
EIP: f2fs_is_valid_blkaddr+0x14b/0x1b0 [f2fs]
 f2fs_iget+0x927/0x1010 [f2fs]
 f2fs_lookup+0x26e/0x630 [f2fs]
 __lookup_slow+0xb3/0x140
 lookup_slow+0x31/0x50
 walk_component+0x185/0x1f0
 path_lookupat+0x51/0x190
 filename_lookup+0x7f/0x140
 user_path_at_empty+0x36/0x40
 vfs_statx+0x61/0xc0
 __do_sys_stat64+0x29/0x40
 sys_stat64+0x13/0x20
 do_fast_syscall_32+0xaa/0x22c
 entry_SYSENTER_32+0x53/0x86

In f2fs_iget(), we will check inode's first block address, if it is valid,
we will set FI_FIRST_BLOCK_WRITTEN flag in inode.

But we should only do this for regular inode, otherwise, like special
inode, i_addr[0] is used for storing device info instead of block address,
it will fail checking flow obviously.

So for non-regular inode, let's skip verifying address and setting flag.

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