drivers/dma/ioat/dma_v2.c: fix warnings

drivers/dma/ioat/dma_v2.c: In function 'ioat2_dma_prep_memcpy_lock':
drivers/dma/ioat/dma_v2.c:680: warning: 'hw' may be used uninitialized in this function
drivers/dma/ioat/dma_v2.c:681: warning: 'desc' may be used uninitialized in this function

Cc: Maciej Sosnowski <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Dan Williams <[e-mail]>

drivers/dma/ioat/dma_v2.c

···
 		/* pass */;
 	else
 		return NULL;
-	for (i = 0; i < num_descs; i++) {
+	i = 0;
+	do {
 		size_t copy = min_t(size_t, len, 1 << ioat->xfercap_log);
 
 		desc = ioat2_get_ring_ent(ioat, idx + i);
···
 		dst += copy;
 		src += copy;
 		dump_desc_dbg(ioat, desc);
-	}
+	} while (++i < num_descs);
 
 	desc->txd.flags = flags;
 	desc->len = total_len;