Fix wait loop and void cast (#24)

* Simplify EINTR/ECANCEL error handling

1. Add semaphore uninterruptible wait function
2 .Replace semaphore wait loop with a single uninterruptible wait
3. Replace all sem_xxx to nxsem_xxx

* Unify the void cast usage

1. Remove void cast for function because many place ignore the returned value witout cast
2. Replace void cast for variable with UNUSED macro

boards/arm/stm32f0l0g0/b-l072z-lrwan1/src/stm32_boot.c

@@ -110,7 +110,7 @@ void board_late_initialize(void)
 #if defined(CONFIG_NSH_LIBRARY) && !defined(CONFIG_LIB_BOARDCTL)
   /* Perform board bring-up here instead of from the board_app_initialize(). */
 
-  (void)stm32_bringup();
+  stm32_bringup();
 #endif
 }
 #endif

boards/arm/stm32f0l0g0/b-l072z-lrwan1/src/stm32_ssd1306.c

@@ -107,7 +107,7 @@ FAR struct lcd_dev_s *board_lcd_getdev(int devno)
 
       /* And turn the OLED on */
 
-      (void)g_lcddev->setpower(g_lcddev, CONFIG_LCD_MAXPOWER);
+      g_lcddev->setpower(g_lcddev, CONFIG_LCD_MAXPOWER);
       return g_lcddev;
     }
 

boards/arm/stm32f0l0g0/b-l072z-lrwan1/src/stm32_sx127x.c

@@ -104,7 +104,7 @@ static int sx127x_irq0_attach(xcpt_t isr, FAR void *arg)
 
   /* IRQ on rising edge */
 
-  (void)stm32_gpiosetevent(GPIO_SX127X_DIO0, true, false, false, isr, arg);
+  stm32_gpiosetevent(GPIO_SX127X_DIO0, true, false, false, isr, arg);
   return OK;
 }