mraa:c Fix dereference of null pointer

Signed-off-by: Cosmin Popescu <gabrielcosmin.popescu@gmail.com>
Signed-off-by: Mihai Tudor Panu <mihai.tudor.panu@intel.com>

src/mraa.c

@@ -192,6 +192,8 @@ imraa_init()
         if (plat != NULL) {
             plat->platform_type = MRAA_NULL_PLATFORM;
             plat->platform_name = "Unknown platform";
+        } else {
+            return MRAA_ERROR_NO_RESOURCES;
         }
     }