block: clean up the check in blkdev_iomap_begin()

It is odd to check the offset amidst a series of assignments. Moving this
check to the beginning of the function makes the code look better.

Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20240625115517.1472120-1-linan666@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Li Nan

block/fops.c

@@ -394,10 +394,11 @@ static int blkdev_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 	struct block_device *bdev = I_BDEV(inode);
 	loff_t isize = i_size_read(inode);
 
-	iomap->bdev = bdev;
-	iomap->offset = ALIGN_DOWN(offset, bdev_logical_block_size(bdev));
 	if (offset >= isize)
 		return -EIO;
+
+	iomap->bdev = bdev;
+	iomap->offset = ALIGN_DOWN(offset, bdev_logical_block_size(bdev));
 	iomap->type = IOMAP_MAPPED;
 	iomap->addr = iomap->offset;
 	iomap->length = isize - iomap->offset;