iwlwifi: mvm: fix off-by-one in scan channels configuration

tail should be equal to the last valid index, so
decrease it by one.

This error causes in "a gap" in some cases (as well as
some possible out-of-bound write), finally resulting in
ucode assertion.

Signed-off-by: Eliad Peller <eliadx.peller@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
diff --git a/drivers/net/wireless/iwlwifi/mvm/scan.c b/drivers/net/wireless/iwlwifi/mvm/scan.c
index cba88a3..c28de54 100644
--- a/drivers/net/wireless/iwlwifi/mvm/scan.c
+++ b/drivers/net/wireless/iwlwifi/mvm/scan.c
@@ -732,7 +732,7 @@
 	int band_2ghz = mvm->nvm_data->bands[IEEE80211_BAND_2GHZ].n_channels;
 	int band_5ghz = mvm->nvm_data->bands[IEEE80211_BAND_5GHZ].n_channels;
 	int head = 0;
-	int tail = band_2ghz + band_5ghz;
+	int tail = band_2ghz + band_5ghz - 1;
 	u32 ssid_bitmap;
 	int cmd_len;
 	int ret;