ext2: fix possible integer truncation in ext2_iomap_begin

For 32-bit architectures we need to cast first_block to u64 before
shifting it left.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Jan Kara <jack@suse.cz>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/ext2/inode.c

@@ -806,7 +806,7 @@ static int ext2_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 
 	iomap->flags = 0;
 	iomap->bdev = inode->i_sb->s_bdev;
-	iomap->offset = first_block << blkbits;
+	iomap->offset = (u64)first_block << blkbits;
 
 	if (ret == 0) {
 		iomap->type = IOMAP_HOLE;