ath5k: Add a function to read chipset's MAC revision

Add bus dependent revision read function which is used to
determine chipset's MAC before hardware is initialized.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Wojciech Dubowik <Wojciech.Dubowik@neratec.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath5k/pci.c b/drivers/net/wireless/ath/ath5k/pci.c
index 3f26cf2..39f0331 100644
--- a/drivers/net/wireless/ath/ath5k/pci.c
+++ b/drivers/net/wireless/ath/ath5k/pci.c
@@ -100,6 +100,12 @@
 	return -ETIMEDOUT;
 }
 
+int ath5k_hw_read_srev(struct ath5k_hw *ah)
+{
+	ah->ah_mac_srev = ath5k_hw_reg_read(ah, AR5K_SREV);
+	return 0;
+}
+
 /* Common ath_bus_opts structure */
 static const struct ath_bus_ops ath_pci_bus_ops = {
 	.ath_bus_type = ATH_PCI,