f2fs: don't call block truncation for aliased file

f2fs: don't call block truncation for aliased file

This patch should avoid the below warning which does not corrupt the metadata
tho.

[   51.508120][  T253] F2FS-fs (dm-59): access invalid blkaddr:36
[   51.508156][  T253]  __f2fs_is_valid_blkaddr+0x330/0x384
[   51.508162][  T253]  f2fs_is_valid_blkaddr_raw+0x10/0x24
[   51.508163][  T253]  f2fs_truncate_data_blocks_range+0x1ec/0x438
[   51.508177][  T253]  f2fs_remove_inode_page+0x8c/0x148
[   51.508194][  T253]  f2fs_evict_inode+0x230/0x76c

Fixes: 128d333f0dff ("f2fs: introduce device aliasing file")
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>