libFLAC/lpc.c: Fix comments

Patch-from: lvqcl <lvqcl.mail@gmail.com>

src/libFLAC/lpc.c

@@ -227,8 +227,8 @@ int FLAC__lpc_quantize_coefficients(const FLAC__real lp_coeff[], unsigned order,
 		}
 	}
 	/* negative shift is very rare but due to design flaw, negative shift is
-	 * a NOP in the decoder, so it must be handled specially by scaling down
-	 * coeffs
+	 * not allowed in the decoder, so it must be handled specially by scaling
+	 * down coeffs
 	 */
 	else {
 		const int nshift = -(*shift);