Fix type warning

ARRAY_SIZE is unsigned, which leads to a warning. Let's fix this by
iterating with an unsigned.

BUG=none
TEST=emerge minigbm

Change-Id: I9b683d19d8ce5208bb4ec25d69292bbefcc4f91d
Reviewed-on: https://chromium-review.googlesource.com/218977
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Tested-by: Stéphane Marchesin <marcheu@chromium.org>
diff --git a/i915.c b/i915.c
index 6daee56..1dd67a0 100644
--- a/i915.c
+++ b/i915.c
@@ -25,7 +25,7 @@
 static int get_gen(int device_id)
 {
 	const uint16_t gen3_ids[] = {0x2582, 0x2592, 0x2772, 0x27A2, 0x27AE, 0x29C2, 0x29B2, 0x29D2, 0xA001, 0xA011};
-	int i;
+	unsigned i;
 	for(i = 0; i < ARRAY_SIZE(gen3_ids); i++)
 		if (gen3_ids[i] == device_id)
 			return 3;