EXI_DeviceMemoryCard: Get rid of magic number in SetCS()

Keeps the code consistent with other usages of the same constant

Source/Core/Core/HW/EXI/EXI_DeviceMemoryCard.cpp

@@ -293,7 +293,7 @@ void CEXIMemoryCard::SetCS(int cs)
       {
         int count = m_uPosition - 5;
         int i = 0;
-        status &= ~0x80;
+        status &= ~MC_STATUS_BUSY;
 
         while (count--)
         {