rtlwifi: fix the wrong size to calculate fifo space

Give correct fifo size to calculate fifo space. Fortunately, the values of
RTL_PCI_MAX_RX_COUNT and TX_DESC_NUM_92E are the same in old code, so it
still works.
Signed-off-by: Steven Ting <steventing@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/realtek/rtlwifi/pci.h

@@ -320,10 +320,10 @@ static inline void pci_write32_async(struct rtl_priv *rtlpriv,
 	writel(val, (u8 __iomem *)rtlpriv->io.pci_mem_start + addr);
 }
 
-static inline u16 calc_fifo_space(u16 rp, u16 wp)
+static inline u16 calc_fifo_space(u16 rp, u16 wp, u16 size)
 {
 	if (rp <= wp)
-		return RTL_PCI_MAX_RX_COUNT - 1 + rp - wp;
+		return size - 1 + rp - wp;
 	return rp - wp - 1;
 }
 

drivers/net/wireless/realtek/rtlwifi/rtl8192ee/trx.c

@@ -498,7 +498,8 @@ u16 rtl92ee_rx_desc_buff_remained_cnt(struct ieee80211_hw *hw, u8 queue_index)
 	if (!start_rx)
 		return 0;
 
-	remind_cnt = calc_fifo_space(read_point, write_point);
+	remind_cnt = calc_fifo_space(read_point, write_point,
+				     RTL_PCI_MAX_RX_COUNT);
 
 	if (remind_cnt == 0)
 		return 0;
@@ -560,7 +561,8 @@ u16 rtl92ee_get_available_desc(struct ieee80211_hw *hw, u8 q_idx)
 	current_tx_write_point = (u16)((tmp_4byte) & 0x0fff);
 
 	point_diff = calc_fifo_space(current_tx_read_point,
-				     current_tx_write_point);
+				     current_tx_write_point,
+				     TX_DESC_NUM_92E);
 
 	rtlpci->tx_ring[q_idx].avl_desc = point_diff;
 	return point_diff;