buffer: cast block to loff_t before shifting it

While sector_t is always defined as a u64 today, that hasn't always been
the case and it might not always be the same size as loff_t in the future.

Link: https://lkml.kernel.org/r/20231109210608.2252323-5-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Pankaj Raghav <p.raghav@samsung.com>
Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: Matthew Wilcox (Oracle)

fs/buffer.c

@@ -2008,7 +2008,7 @@ static int
 iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
 		const struct iomap *iomap)
 {
-	loff_t offset = block << inode->i_blkbits;
+	loff_t offset = (loff_t)block << inode->i_blkbits;
 
 	bh->b_bdev = iomap->bdev;