examples: quiet -Wshorten-64-to-32 warnings

all around usage of strtol/strtoul

ported from libvpx:
08b8b6bb8 examples: quiet -Wshorten-64-to-32 warnings

Change-Id: If907c89f107a068987aa71ddd93cee9a7389e4cd
diff --git a/examples/aom_cx_set_ref.c b/examples/aom_cx_set_ref.c
index 6beb4fb..d1aec99 100644
--- a/examples/aom_cx_set_ref.c
+++ b/examples/aom_cx_set_ref.c
@@ -342,8 +342,8 @@
   }
 
   info.codec_fourcc = encoder->fourcc;
-  info.frame_width = strtol(width_arg, NULL, 0);
-  info.frame_height = strtol(height_arg, NULL, 0);
+  info.frame_width = (int)strtol(width_arg, NULL, 0);
+  info.frame_height = (int)strtol(height_arg, NULL, 0);
   info.time_base.numerator = 1;
   info.time_base.denominator = fps;