t/zbd: Fix pass condition of test case #3

t/zbd: Fix pass condition of test case #3

The test case #3 checks that the read workload for empty zones ends
without reading any data. When zonemode=zbd, it is expected for both
regular block devices and zoned block devices. However, the test case
allowed for regular block devices to read data from empty zones. Remove
this special pass condition for regular block devices.

Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>