libext2fs: fix off-by-one error in file truncation

libext2fs: fix off-by-one error in file truncation

When told to truncate a file, ext2fs_file_set_size2() should start with
the first block past the end of the file.  The current calculation
jumps one more block ahead, with the result that it fails to hack off
the last block.  Adding blocksize-1 and dividing is sufficient to find
the last block.

Reviewed-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>