rlc: Use sizeof() for the memset instead of ARRAY_SIZE

In this case both will give the same result but it is better to use
sizeof. But it is better to use the raw number of bytes instead of
the number of elements.

src/rlc.cpp

@@ -28,7 +28,7 @@ extern "C" {
 uint8_t *gprs_rlc_data::prepare(size_t block_data_len)
 {
 	/* todo.. only set it once if it turns out to be a bottleneck */
-	memset(block, 0x0, ARRAY_SIZE(block));
+	memset(block, 0x0, sizeof(block));
 	memset(block, 0x2b, block_data_len);
 
 	return block;