stmhal: Fix HAL error raising; make test for it.

Addresses issue #968.

stmhal/mphal.c

@@ -16,5 +16,5 @@ const byte mp_hal_status_to_errno_table[4] = {
 };
 
 NORETURN void mp_hal_raise(HAL_StatusTypeDef status) {
-    nlr_raise(mp_obj_new_exception_arg1(&mp_type_OSError, (mp_obj_t)(mp_uint_t)mp_hal_status_to_errno_table[status]));
+    nlr_raise(mp_obj_new_exception_arg1(&mp_type_OSError, MP_OBJ_NEW_SMALL_INT(mp_hal_status_to_errno_table[status])));
 }

tests/pyb/halerror.py

+# test hal errors
+
+import pyb
+
+i2c = pyb.I2C(2, pyb.I2C.MASTER)
+try:
+    i2c.recv(1, 1)
+except OSError as e:
+    print(repr(e))
+
+can = pyb.CAN(1, pyb.CAN.NORMAL)
+try:
+    can.send('1', 1, timeout=50)
+except OSError as e:
+    print(repr(e))

tests/pyb/halerror.py.exp

+OSError(5,)
+OSError(116,)