Cycles: Fix for non-vectorized version of bitscan()

It was doing bit search in an opposite direction comparing to a
vectorized version.

intern/cycles/util/util_simd.h

@@ -454,13 +454,12 @@ ccl_device_inline int bitscan(int value)
 {
 	assert(value != 0);
 	int bit = 0;
-	while(value >>= 1) {
+	while((value & (1 << bit)) == 0) {
 		++bit;
 	}
 	return bit;
 }
 
-
 #endif /* __KERNEL_SSE2__ */
 
 /* quiet unused define warnings */