turnip: clearValueCount member of VkRenderPassBeginInfo can be zero
According to the spec, it can be zero if no attachment has load_op_clear.
Fixes crash on:
dEQP-VK.renderpass.suballocation.multisample.r5g6b5_unorm_pack16.samples_2 dEQP-VK.renderpass.suballocation.multisample.d16_unorm.samples_2
Signed-off-by: Samuel Iglesias Gonsálvez siglesias@igalia.com