boards: cxd56xx: Refactor cxd56_gs2200m.c

Summary:
- This commit refactors cxd56_gs2200m.c
- gs2200m_irq_enable() and gs2200m_irq_disable() are now symmetric.

Impact:
- All use cases which use the gs2200m driver.

Testing:
- Tested with spresense:wifi

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

boards/arm/cxd56xx/common/src/cxd56_gs2200m.c

@@ -116,20 +116,13 @@ static void gs2200m_irq_enable(void)
 
   wlinfo("== ec:%d called=%d \n", _enable_count, _n_called++);
 
-  if (1 == _enable_count)
-    {
-      /* NOTE: This would happen if we received an event */
-
-      return;
-    }
-
-  _enable_count++;
-
-  if (1 == _enable_count)
+  if (0 == _enable_count)
     {
       cxd56_gpioint_enable(PIN_UART2_CTS);
     }
 
+  _enable_count++;
+
   spin_unlock_irqrestore(flags);
 }