Changed every memcmp to SCA equivalent mbedtls_platform_memcmp

This makes physical attacks more difficult.
Selftest memcmp functions were not changed.
diff --git a/library/base64.c b/library/base64.c
index f06b57b..1e9f6d7 100644
--- a/library/base64.c
+++ b/library/base64.c
@@ -260,7 +260,7 @@
     src = base64_test_dec;
 
     if( mbedtls_base64_encode( buffer, sizeof( buffer ), &len, src, 64 ) != 0 ||
-         memcmp( base64_test_enc, buffer, 88 ) != 0 )
+            memcmp( base64_test_enc, buffer, 88 ) != 0 )
     {
         if( verbose != 0 )
             mbedtls_printf( "failed\n" );
@@ -274,7 +274,7 @@
     src = base64_test_enc;
 
     if( mbedtls_base64_decode( buffer, sizeof( buffer ), &len, src, 88 ) != 0 ||
-         memcmp( base64_test_dec, buffer, 64 ) != 0 )
+            memcmp( base64_test_dec, buffer, 64 ) != 0 )
     {
         if( verbose != 0 )
             mbedtls_printf( "failed\n" );