template.c: simplify file_length calculation

src/template.c

@@ -181,14 +181,11 @@ main(void)
 	// 2. prepare variables
 	uint32_t buffer_size = PRODUCT,
 		file_length =
-			4 * 4   /* 4 strings of 4 characters */ +
-			5 * 4   /* 5 uint32_t values */         +
-			4 * 2   /* 4 uint16_t values */         +
-			PRODUCT /* sample data */
-
-			/* subtract Subchunk2 headers: */
-			- 4 /* a string of 4 characters */
-			- 4 /* a uint32_t value */,
+			/* file length without "RIFF" chunk */
+			3 * 4   /* 3 strings of 4 characters: "WAVE", "fmt ", "data" */ +
+			4 * 4   /* 4 uint32_t values */ +
+			4 * 2   /* 4 uint16_t values */ +
+			PRODUCT /* sample data */,
 		fmt_data_length = 16 /* <--
 		 * length of format data before this value
 		 * in the file format structure