Revert "radv: remove unnecessary memset() in radv_AllocateCommandBuffers()"

Revert "radv: remove unnecessary memset() in radv_AllocateCommandBuffers()"

This fixes two CTS regressions:
- dEQP-VK.api.object_management.alloc_callback_fail_multiple.command_buffer_primary
- dEQP-VK.api.object_management.alloc_callback_fail_multiple.command_buffer_secondary

These two tests are part the mustpass lists, so presumably they
are correct and my change was wrong.

This reverts commit 0f68208f1d1d3b7b2963dab40e84c60212518692.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>