block: remove an incorrect check from blk_rq_append_bio

blk_rq_append_bio is also used for the copy case, not just the map case,
so tis debug check is not correct.

Fixes: 393bb12e ("block: stop calling blk_queue_bounce for passthrough requests")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Link: https://lore.kernel.org/r/20210409150447.1977410-1-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>