vpxdec: normalize frame size types

int -> size_t for threshold values. this silences a few signed/unsigned
comparison warnings

Change-Id: Ic7b7af61f75f60a1b6d04167640cea2d09bbd967

vpxdec.c

diff --git a/vpxdec.c b/vpxdec.c
index 6d5ca24..98d1550 100644
--- a/vpxdec.c
+++ b/vpxdec.c
@@ -187,8 +187,8 @@
     if (!feof(infile))
       warn("Failed to read RAW frame size\n");
   } else {
-    const int kCorruptFrameThreshold = 256 * 1024 * 1024;
-    const int kFrameTooSmallThreshold = 256 * 1024;
+    const size_t kCorruptFrameThreshold = 256 * 1024 * 1024;
+    const size_t kFrameTooSmallThreshold = 256 * 1024;
     frame_size = mem_get_le32(raw_hdr);
 
     if (frame_size > kCorruptFrameThreshold) {