zbd: Check for direct flag only if its block device

zbd: Check for direct flag only if its block device

nvme-ns generic character devices currently do not support O_DIRECT flag.
Check for fio option for direct flag only if filetype is a block device.

t/zbd skip test case #1 for character devices as they don't require
direct I/O.

Tested-by: Vincent Fu <vincent.fu@samsung.com>
Signed-off-by: Ankit Kumar <ankit.kumar@samsung.com>
Reviewed-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Link: https://lore.kernel.org/r/20220531133155.17493-8-ankit.kumar@samsung.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>