scsi: sd_zbc: Fix sd_zbc_check_zone_size() error path

If a drive with variable zone sizes or an invalid last zone size is
detected, the local variable this_zone_blocks is set to 0 and early return
from the function triggered, but this does not result in an error return.
The local variable zone_blocks must be set to 0 for an error to be
returned.

[mkp: typo in commit description]

Fixes: ccce20fc

 ("scsi: sd_zbc: Avoid that resetting a zone fails sporadically")
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>