udf: use sector_t and loff_t for file offsets

Use sector_t and loff_t for file offsets in UDF filesystem.  Otherwise an
overflow may occur for long files.  Also make inode_bmap() return offset in
the extent in number of blocks instead of number of bytes - for most
callers this is more convenient.

Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>