libext2fs: fix unaligned, multiblock writes in the unix_io handler

The read-modify-write code for the unaligned fallback code wasn't
working for multi-block writes.  This was unmasked by FreeBSD 11-rc2,
since its malloc() is returning unaligned memory regions for large
memory regions.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

lib/ext2fs/unix_io.c

@@ -300,6 +300,7 @@ static errcode_t raw_write_blk(io_channel channel,
 			goto short_write;
 		size -= actual;
 		buf += actual;
+		location += actual;
 	}
 	return 0;