Replace instances of byte reading macros with PUT

Instances of a group of byte reading macros which are equivilant to
MBEDTLS_PUT_UINTx_yz

Signed-off-by: Joe Subbiani <joe.subbiani@arm.com>
diff --git a/library/ssl_cookie.c b/library/ssl_cookie.c
index b226033..071e55e 100644
--- a/library/ssl_cookie.c
+++ b/library/ssl_cookie.c
@@ -166,10 +166,7 @@
     t = ctx->serial++;
 #endif
 
-    (*p)[0] = MBEDTLS_BYTE_3( t );
-    (*p)[1] = MBEDTLS_BYTE_2( t );
-    (*p)[2] = MBEDTLS_BYTE_1( t );
-    (*p)[3] = MBEDTLS_BYTE_0( t );
+    MBEDTLS_PUT_UINT32_BE(t, *p, 0);
     *p += 4;
 
 #if defined(MBEDTLS_THREADING_C)