radv: assert that colorAttachment is valid for CmdClearAttachment

radv: assert that colorAttachment is valid for CmdClearAttachment

This partially reverts a change from b7a93cbdede05a ("radv: Handle
VK_ATTACHMENT_UNUSED in CmdClearAttachment") which fixed actual issues
but also started to accept invalid values for the colorAttachment
field.

This change asserts that the field is valid for the current pass.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: b7a93cbdede05a ("radv: Handle VK_ATTACHMENT_UNUSED in CmdClearAttachment")
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>