iomap: Fix unsharing of an extent >2GB on a 32-bit machine

Widen the type used for counting the number of bytes unshared.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/iomap/buffered-io.c

@@ -909,7 +909,7 @@ iomap_unshare_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 		struct iomap *iomap, struct iomap *srcmap)
 {
 	long status = 0;
-	ssize_t written = 0;
+	loff_t written = 0;
 
 	/* don't bother with blocks that are not shared to start with */
 	if (!(iomap->flags & IOMAP_F_SHARED))