ath9k: Fix lockdep splat

ath9k: Fix lockdep splat

Cancel the MCI work only when MCI is actually enabled.
Fixes this:

[96833.124051] Call Trace:
[96833.124060]  [<ffffffff810afaf8>] __lock_acquire+0x1518/0x1e40
[96833.124065]  [<ffffffff810ad126>] ? mark_held_locks+0x86/0x110
[96833.124069]  [<ffffffff810ad3ad>] ? trace_hardirqs_on+0xd/0x10
[96833.124073]  [<ffffffff814464f0>] ? _raw_spin_unlock_irq+0x30/0x70
[96833.124078]  [<ffffffff81072968>] ? wait_on_cpu_work+0x98/0xc0
[96833.124082]  [<ffffffff810b0a11>] lock_acquire+0xa1/0x150
[96833.124085]  [<ffffffff81072990>] ? wait_on_cpu_work+0xc0/0xc0
[96833.124088]  [<ffffffff81072990>] ? wait_on_cpu_work+0xc0/0xc0
[96833.124092]  [<ffffffff810729e2>] wait_on_work+0x52/0x120
[96833.124095]  [<ffffffff81072990>] ? wait_on_cpu_work+0xc0/0xc0
[96833.124099]  [<ffffffff81063b3f>] ? del_timer+0x7f/0x110
[96833.124102]  [<ffffffff81072c13>] __cancel_work_timer+0x83/0x130
[96833.124106]  [<ffffffff81072cf0>] cancel_work_sync+0x10/0x20
[96833.124113]  [<ffffffffa065b5cd>] __ath_cancel_work+0x4d/0x60 [ath9k]
[96833.124119]  [<ffffffffa065cf28>] ath9k_config+0x458/0x680 [ath9k]
[96833.124125]  [<ffffffffa065dd1e>] ? ath9k_flush+0x6e/0x1d0 [ath9k]
[96833.124129]  [<ffffffff8144394d>] ? __mutex_unlock_slowpath+0x10d/0x190
[96833.124146]  [<ffffffffa056c7b5>] ieee80211_hw_config+0x135/0x2a0 [mac80211]
[96833.124163]  [<ffffffffa057ebbb>] ieee80211_do_open+0x67b/0xc50 [mac80211]
[96833.124178]  [<ffffffffa057f1fd>] ieee80211_open+0x6d/0x80 [mac80211]
[96833.124183]  [<ffffffff8137a44f>] __dev_open+0x9f/0xf0
[96833.124187]  [<ffffffff8137a701>] __dev_change_flags+0xa1/0x180
[96833.124190]  [<ffffffff8137a898>] dev_change_flags+0x28/0x70
[96833.124195]  [<ffffffff813e1179>] devinet_ioctl+0x659/0x780
[96833.124199]  [<ffffffff8137aea0>] ? dev_ioctl+0x210/0x6d0
[96833.124203]  [<ffffffff813e1db5>] inet_ioctl+0x75/0x90
[96833.124208]  [<ffffffff8135e0e0>] sock_do_ioctl+0x30/0x70
[96833.124211]  [<ffffffff8135e3dd>] sock_ioctl+0x7d/0x2c0
[96833.124218]  [<ffffffff81193c39>] do_vfs_ioctl+0x99/0x580
[96833.124222]  [<ffffffff81447415>] ? sysret_check+0x22/0x5d
[96833.124226]  [<ffffffff811941b9>] sys_ioctl+0x99/0xa0
[96833.124230]  [<ffffffff814473e9>] system_call_fastpath+0x16/0x1b

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>