ath9k: Cleanup MCI init/deinit routines

ath9k: Cleanup MCI init/deinit routines

This patch simplifies the buffer allocation functions
for MCI and removes unneeded memset calls. Also, a couple
of unused variables are removed and a memory leak in DMA
allocation is fixed.

[ 1263.788267] WARNING: at /home/sujith/dev/wireless-testing/lib/dma-debug.c:875 check_unmap+0x173/0x7e0()
[ 1263.788273] ath9k 0000:06:00.0: DMA-API: device driver frees DMA memory with different size
               [device address=0x0000000071908000] [map size=512 bytes] [unmap size=256 bytes]
[ 1263.788345] Pid: 774, comm: rmmod Tainted: G        W  O 3.3.0-rc3-wl #18
[ 1263.788348] Call Trace:
[ 1263.788355]  [<ffffffff8105110f>] warn_slowpath_common+0x7f/0xc0
[ 1263.788359]  [<ffffffff81051206>] warn_slowpath_fmt+0x46/0x50
[ 1263.788363]  [<ffffffff8125a713>] check_unmap+0x173/0x7e0
[ 1263.788368]  [<ffffffff8123fc22>] ? prio_tree_left+0x32/0xc0
[ 1263.788373]  [<ffffffff8125aded>] debug_dma_free_coherent+0x6d/0x80
[ 1263.788381]  [<ffffffffa0701c3c>] ath_mci_cleanup+0x7c/0x110 [ath9k]
[ 1263.788387]  [<ffffffffa06f4033>] ath9k_deinit_softc+0x113/0x120 [ath9k]
[ 1263.788392]  [<ffffffffa06f55cc>] ath9k_deinit_device+0x5c/0x70 [ath9k]
[ 1263.788397]  [<ffffffffa0704934>] ath_pci_remove+0x54/0xa0 [ath9k]
[ 1263.788401]  [<ffffffff81267d06>] pci_device_remove+0x46/0x110
[ 1263.788406]  [<ffffffff813102bc>] __device_release_driver+0x7c/0xe0
[ 1263.788410]  [<ffffffff81310a00>] driver_detach+0xd0/0xe0
[ 1263.788414]  [<ffffffff81310118>] bus_remove_driver+0x88/0xe0
[ 1263.788418]  [<ffffffff813111c2>] driver_unregister+0x62/0xa0
[ 1263.788421]  [<ffffffff812680c4>] pci_unregister_driver+0x44/0xc0
[ 1263.788427]  [<ffffffffa0705015>] ath_pci_exit+0x15/0x20 [ath9k]
[ 1263.788432]  [<ffffffffa070a92d>] ath9k_exit+0x15/0x31 [ath9k]
[ 1263.788436]  [<ffffffff810b971c>] sys_delete_module+0x18c/0x270
[ 1263.788441]  [<ffffffff81436edd>] ? retint_swapgs+0x13/0x1b
[ 1263.788446]  [<ffffffff812483be>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[ 1263.788450]  [<ffffffff814378e9>] system_call_fastpath+0x16/0x1b
[ 1263.788453] ---[ end trace 3ab4d030ffde40d4 ]---

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