ioatdma: silence GCC warnings

Building dma_v3.o triggers a GCC warning:
    drivers/dma/ioat/dma_v3.c: In function ‘__ioat3_prep_pq16_lock’:
    drivers/dma/ioat/dma_v3.c:264:11: warning: array subscript is below array bounds [-Warray-bounds]
    drivers/dma/ioat/dma_v3.c:264:11: warning: array subscript is below array bounds [-Warray-bounds]

This warning is caused by pq16_set_src(). It uses "int idx" as an index
to an eight element array. Changing "idx" to "unsigned" silences this
warning. Apparently GCC can then determine that "idx" will never be
negative.
Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Acked-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dan Williams <djbw@fb.com>

drivers/dma/ioat/dma_v3.c

@@ -251,7 +251,7 @@ static bool is_bwd_noraid(struct pci_dev *pdev)
 }
 
 static void pq16_set_src(struct ioat_raw_descriptor *desc[3],
-			dma_addr_t addr, u32 offset, u8 coef, int idx)
+			dma_addr_t addr, u32 offset, u8 coef, unsigned idx)
 {
 	struct ioat_pq_descriptor *pq = (struct ioat_pq_descriptor *)desc[0];
 	struct ioat_pq16a_descriptor *pq16 =