panvk: fix typo in scissor calculation for CSF
Fixes dEQP-VK.draw.renderpass.scissor.*
Test run totals:
Passed: 16/22 (72.7%)
Failed: 0/22 (0.0%)
Not supported: 6/22 (27.3%)
Warnings: 0/22 (0.0%)
Waived: 0/22 (0.0%)