ath9k_hw: Fix invalid MCI GPM index access/caching

There is a possibility that AR_MCI_GPM_1 register can
return 0xdeadbeef and this results in caching of invalid
GPM index in ar9003_mci_is_gpm_valid. Ensure we
have appropriate checks to avoid this.

Cc: xijin luo <xijin@qca.qualcomm.com>
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/ar9003_mci.c

@@ -1321,6 +1321,10 @@ u32 ar9003_mci_get_next_gpm_offset(struct ath_hw *ah, bool first, u32 *more)
 
 	if (first) {
 		gpm_ptr = MS(REG_READ(ah, AR_MCI_GPM_1), AR_MCI_GPM_WRITE_PTR);
+
+		if (gpm_ptr >= mci->gpm_len)
+			gpm_ptr = 0;
+
 		mci->gpm_idx = gpm_ptr;
 		return gpm_ptr;
 	}
@@ -1365,6 +1369,10 @@ u32 ar9003_mci_get_next_gpm_offset(struct ath_hw *ah, bool first, u32 *more)
 			more_gpm = MCI_GPM_NOMORE;
 
 		temp_index = mci->gpm_idx;
+
+		if (temp_index >= mci->gpm_len)
+			temp_index = 0;
+
 		mci->gpm_idx++;
 
 		if (mci->gpm_idx >= mci->gpm_len)