Fix some dosctrings errors and trailing whitespaces

Signed-off-by: Kirill Luchikhin <kirill.luchikhin@intel.com>

src/pulsensor/pulsensor.h

@@ -63,7 +63,7 @@ struct pulsensor_context {
     uint8_t          pin;
     uint8_t          ret;
     mraa_aio_context  pin_ctx;
-    
+
     callback_handler callback;
 };