Fix fpga memory scalar access test to use correct highest address

Change-Id: I24b22a11cbbb75363e9d0e1ccdc6519e23522608

test/vx/test_fpga_memory_scalar_access.cpp

@@ -25,7 +25,7 @@ void start(void)
 	test_write_read<uint8_t>(123);
 	test_write_read<uint16_t>(12345);
 	test_write_read<uint32_t>(12345678);
-	test_write_read<uint8_t>(17 + 4, 1 << 29); // w/r highest extmem address
+	test_write_read<uint8_t>(17 + 4, 0x20000 - 1); // w/r highest extmem address
 	testcase_end();
 
 	test_summary();