soc: qcom: llcc-slice: Add error checks for API functions

llcc_slice_getd can return a ERR_PTR code on failure. Add a IS_ERR_OR_NULL
check to subsequent API calls that use struct llcc_slice_desc to guard
against faults and to let the leaf drivers get away with safely using a
ERR_PTR() encoded "pointer" in the aftermath of a llcc_slice_getd error.

Signed-off-by: Jordan Crouse <[e-mail]>
Reviewed-by: Vivek Gautam <[e-mail]>
Signed-off-by: Andy Gross <[e-mail]>

drivers/soc/qcom/llcc-slice.c

···
  */
 void llcc_slice_putd(struct llcc_slice_desc *desc)
 {
-	kfree(desc);
+	if (!IS_ERR_OR_NULL(desc))
+		kfree(desc);
 }
 EXPORT_SYMBOL_GPL(llcc_slice_putd);
 
···
 	int ret;
 	u32 act_ctrl_val;
 
+	if (IS_ERR_OR_NULL(desc))
+		return -EINVAL;
+
 	mutex_lock(&drv_data->lock);
 	if (test_bit(desc->slice_id, drv_data->bitmap)) {
 		mutex_unlock(&drv_data->lock);
···
 	u32 act_ctrl_val;
 	int ret;
 
+	if (IS_ERR_OR_NULL(desc))
+		return -EINVAL;
+
 	mutex_lock(&drv_data->lock);
 	if (!test_bit(desc->slice_id, drv_data->bitmap)) {
 		mutex_unlock(&drv_data->lock);
···
  */
 int llcc_get_slice_id(struct llcc_slice_desc *desc)
 {
+	if (IS_ERR_OR_NULL(desc))
+		return -EINVAL;
+
 	return desc->slice_id;
 }
 EXPORT_SYMBOL_GPL(llcc_get_slice_id);
···
  */
 size_t llcc_get_slice_size(struct llcc_slice_desc *desc)
 {
+	if (IS_ERR_OR_NULL(desc))
+		return 0;
+
 	return desc->slice_size;
 }
 EXPORT_SYMBOL_GPL(llcc_get_slice_size);