iommu/vt-d: Fix signedness bug in alloc_irte()

"index" needs to be signed for the error handling to work.  I deleted a
little bit of obsolete cruft related to "index" and "start_index" as
well.

Fixes: 360eb3c568 ('iommu/vt-d: use dedicated bitmap to track remapping entry allocation status')

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>

drivers/iommu/intel_irq_remapping.c

@@ -71,18 +71,13 @@ static int alloc_irte(struct intel_iommu *iommu, int irq, u16 count)
 	struct ir_table *table = iommu->ir_table;
 	struct irq_2_iommu *irq_iommu = irq_2_iommu(irq);
 	struct irq_cfg *cfg = irq_get_chip_data(irq);
-	u16 index, start_index;
 	unsigned int mask = 0;
 	unsigned long flags;
+	int index;
 
 	if (!count || !irq_iommu)
 		return -1;
 
-	/*
-	 * start the IRTE search from index 0.
-	 */
-	index = start_index = 0;
-
 	if (count > 1) {
 		count = __roundup_pow_of_two(count);
 		mask = ilog2(count);