ath9k: Fix a WARNING on suspend/resume with IBSS

this patch is dependent on the patch "cfg80211: fix interface
combinations"

In ath9k currently we have ADHOC interface as a single incompatible
interface. when drv_add_interface is called during resume we got to
consider number of vifs already present in addition to checking the
drivers 'opmode' information about ADHOC.  we incorrectly assume
an ADHOC interface is already present. Then we may miss some driver
specific data for the ADHOC interface after resume.

The above mentioned checks can be removed from the driver,
as the patch 'cfg80211: fix interface combinations' ensures that
if an interface type is not advertised by the driver in any of the
interface combinations(via ieee80211_iface_combination) then it shall
be treated as a single incompatible interface. Fixes the following
warning on suspend/resume with ibss interface.

        ath: phy0: Cannot create ADHOC interface when other
        interfaces already exist.
        WARNING: at net/mac80211/driver-ops.h:12
        ieee80211_reconfig+0x1882/0x1ca0 [mac80211]()
        Hardware name: 2842RK1
        wlan2:  Failed check-sdata-in-driver check, flags: 0x0

        Call Trace:
        [<c01361b2>] warn_slowpath_common+0x72/0xa0
        [<f8aaa7c2>] ? ieee80211_reconfig+0x1882/0x1ca0
        [mac80211]
        [<f8aaa7c2>] ? ieee80211_reconfig+0x1882/0x1ca0
        [mac80211]
        [<c0136283>] warn_slowpath_fmt+0x33/0x40
        [<f8aaa7c2>] ieee80211_reconfig+0x1882/0x1ca0 [mac80211]
        [<c06c1d1a>] ? mutex_lock_nested+0x23a/0x2f0
        [<f8a95097>] ieee80211_resume+0x27/0x70 [mac80211]
        [<fd177edf>] wiphy_resume+0x8f/0xa0 [cfg80211]

Cc: stable@vger.kernel.org
Cc: Rajkumar Manoharan <rmanohar@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/main.c

@@ -1443,15 +1443,6 @@ static int ath9k_add_interface(struct ieee80211_hw *hw,
 		}
 	}
 
-	if ((ah->opmode == NL80211_IFTYPE_ADHOC) ||
-	    ((vif->type == NL80211_IFTYPE_ADHOC) &&
-	     sc->nvifs > 0)) {
-		ath_err(common, "Cannot create ADHOC interface when other"
-			" interfaces already exist.\n");
-		ret = -EINVAL;
-		goto out;
-	}
-
 	ath_dbg(common, CONFIG, "Attach a VIF of type: %d\n", vif->type);
 
 	sc->nvifs++;