bitstream,mem_put_varsize: quiet warning in assert

string literal to int

BUG=aomedia:445

Change-Id: I262911ad4e4b52f2d203c03d9bdfcbaa1a81984b

av1/encoder/bitstream.c

@@ -5068,7 +5068,7 @@ static void mem_put_varsize(uint8_t *const dst, const int sz, const int val) {
     case 2: mem_put_le16(dst, val); break;
     case 3: mem_put_le24(dst, val); break;
     case 4: mem_put_le32(dst, val); break;
-    default: assert("Invalid size" && 0); break;
+    default: assert(0 && "Invalid size"); break;
   }
 }
 static int remux_tiles(const AV1_COMMON *const cm, uint8_t *dst,