Cast value to avoid size_t/int warning on win64

dboolhuff.c(50) : warning C4267: 'initializing' : conversion from
'size_t' to 'int'

Change-Id: I6b85759efb2fa19f362f406623d8a7583a55c036
diff --git a/vp8/decoder/dboolhuff.c b/vp8/decoder/dboolhuff.c
index 546fb2d..0007d7a 100644
--- a/vp8/decoder/dboolhuff.c
+++ b/vp8/decoder/dboolhuff.c
@@ -47,8 +47,8 @@
     unsigned char decrypted[sizeof(VP8_BD_VALUE) + 1];
 
     if (br->decrypt_cb) {
-        int n = bytes_left > sizeof(decrypted) ? sizeof(decrypted) : bytes_left;
-        br->decrypt_cb(br->decrypt_state, bufptr, decrypted, n);
+        size_t n = bytes_left > sizeof(decrypted) ? sizeof(decrypted) : bytes_left;
+        br->decrypt_cb(br->decrypt_state, bufptr, decrypted, (int)n);
         bufptr = decrypted;
     }