Don't chain assignments of vars of different types

Don't chain assignments of variables of different types. In this case,
the first assigned variable is of type uint64_t, which is of a larger
size than the second assigned variable of type int, so Visual Studio
2017 warns:

aom\aom_scale\generic\yv12config.c(196): warning C4244:
'=': conversion from 'uint64_t' to 'int', possible loss of data

Change-Id: If2a50cc250ed264603feaba9b0ebe64824fe4ae1

aom_scale/generic/yv12config.c

diff --git a/aom_scale/generic/yv12config.c b/aom_scale/generic/yv12config.c
index ac269e7..b425781 100644
--- a/aom_scale/generic/yv12config.c
+++ b/aom_scale/generic/yv12config.c
@@ -193,7 +193,8 @@
   *yplane_size =
       (aligned_height + 2 * border) * (uint64_t)(*y_stride) + byte_alignment;
 
-  *uv_stride = *uvplane_size = 0;
+  *uv_stride = 0;
+  *uvplane_size = 0;
   if (is_monochrome == 0) {
     *uv_stride = *y_stride >> ss_x;
     *uvplane_size =