make the HAL sleep function obey the chip documentation

the sleep mode doesn't get set immediately, and needs to be waited upon.

watch-library/hardware/hal/include/hpl_sleep.h

@@ -70,6 +70,16 @@ extern "C" {
  */
 int32_t _set_sleep_mode(const uint8_t mode);
 
+/**
+ * \brief Get the sleep mode for the device
+ *
+ * This function gets the sleep mode for the device.
+ *
+ * \return the current value of the sleep mode configuration bits
+ */
+int32_t _get_sleep_mode(void);
+
+
 /**
  * \brief Reset MCU
  */

watch-library/hardware/hal/src/hal_sleep.c

@@ -57,6 +57,9 @@ int sleep(const uint8_t mode)
 	if (ERR_NONE != _set_sleep_mode(mode))
 		return ERR_INVALID_ARG;
 
+        // wait for the mode set to actually take, per chip doc.
+        while(_get_sleep_mode() != mode);
+
 	_go_to_sleep();
 
 	return ERR_NONE;

watch-library/hardware/hpl/pm/hpl_pm.c

@@ -63,6 +63,14 @@ int32_t _set_sleep_mode(const uint8_t mode)
 	return ERR_NONE;
 }
 
+/**
+ * \brief Get the sleep mode for the device
+ */
+int32_t _get_sleep_mode()
+{
+    return hri_pm_read_SLEEPCFG_SLEEPMODE_bf(PM);
+}
+
 /**
  * \brief Set performance level
  */