api/platform_name: Change return when null platform

Easier to error check against

Signed-off-by: Thomas Ingleby <thomas.c.ingleby@intel.com>

api/mraa/common.h

@@ -237,7 +237,7 @@ unsigned int mraa_adc_supported_bits();
 mraa_result_t mraa_set_log_level(int level);
 
 /**
- * Return the Platform's Name, If no platform detected return "Unknown"
+ * Return the Platform's Name, If no platform detected return NULL
  *
  * @return platform name
  */

api/mraa/common.hpp

@@ -117,7 +117,7 @@ inline unsigned int adcSupportedBits()
 }
 
 /**
- * Return Platform Name. "Unknown" if no platform inited.
+ * Return Platform Name. Returns NULL if no platform inited.
  *
  * @return platform name
  */

src/mraa.c

@@ -303,8 +303,9 @@ mraa_adc_supported_bits()
 char*
 mraa_get_platform_name()
 {
-    if (plat == NULL)
-        return "Unknown";
+    if (plat == NULL) {
+        return NULL;
+    }
     return (char*) plat->platform_name;
 }