drm/i915/guc: Don't GEM_BUG_ON on corrupted H2G CTB

{

	struct intel_guc_ct_buffer *ctb = &ct->ctbs[CTB_SEND];

	struct guc_ct_buffer_desc *desc = ctb->desc;

	u32 head = desc->head / 4;	/* in dwords */

	u32 tail = desc->tail / 4;	/* in dwords */

	u32 size = desc->size / 4;	/* in dwords */

	u32 used;			/* in dwords */

	u32 head = desc->head;

	u32 tail = desc->tail;

	u32 size = desc->size;

	u32 used;

	u32 header;

	u32 *cmds = ctb->cmds;

	unsigned int i;

	GEM_BUG_ON(desc->size % 4);

	GEM_BUG_ON(desc->head % 4);

	GEM_BUG_ON(desc->tail % 4);

	GEM_BUG_ON(tail >= size);

	if (unlikely(desc->is_in_error))

		return -EPIPE;

	if (unlikely(!IS_ALIGNED(head | tail | size, 4) ||

		     (tail | head) >= size))

		goto corrupted;

	/* later calculations will be done in dwords */

	head /= 4;

	tail /= 4;

	size /= 4;

	/*

	 * tail == head condition indicates empty. GuC FW does not support

		cmds[tail] = action[i];

		tail = (tail + 1) % size;

	}

	GEM_BUG_ON(tail > size);

	/* now update desc tail (back in bytes) */

	desc->tail = tail * 4;

	GEM_BUG_ON(desc->tail > desc->size);

	return 0;

corrupted:

	CT_ERROR(ct, "Corrupted descriptor addr=%#x head=%u tail=%u size=%u\n",

		 desc->addr, desc->head, desc->tail, desc->size);

	desc->is_in_error = 1;

	return -EPIPE;

}

/**