Test SPISlave \\ Current lib. does not work on STM32F446RE

Revision:
0:8f9f2c56e597
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed-os.lib	Sat Nov 18 10:15:30 2017 +0000
@@ -0,0 +1,1 @@
+https://github.com/ARMmbed/mbed-os/#78474a5129e18e136cc7e872adbaa5b74fbb8f6a