iwlwifi: fix DMA allocation warnings

iwlwifi: fix DMA allocation warnings

Below warning is triggered sometimes at module removal time when
CONFIG_DMA_API_DEBUG is enabled. This should be caused by we didn't
unmap pending commands (enqueued, but no complete notification
received) for the Tx command queue.

[ 1583.107469] ------------[ cut here ]------------
[ 1583.107539] WARNING: at lib/dma-debug.c:688
dma_debug_device_change+0x13c/0x180()
[ 1583.107617] Hardware name: ...
[ 1583.107664] pci 0000:04:00.0: DMA-API: device driver has pending DMA
allocations while released from device [count=1]
[ 1583.107713] Modules linked in: ...
[ 1583.111661] Pid: 16970, comm: modprobe Tainted: G        W
2.6.34-rc1-wl #33
[ 1583.111727] Call Trace:
[ 1583.111779]  [<c02a281c>] ? dma_debug_device_change+0x13c/0x180
[ 1583.111833]  [<c02a281c>] ? dma_debug_device_change+0x13c/0x180
[ 1583.111908]  [<c0138e11>] warn_slowpath_common+0x71/0xd0
[ 1583.111963]  [<c02a281c>] ? dma_debug_device_change+0x13c/0x180
[ 1583.112016]  [<c0138ebb>] warn_slowpath_fmt+0x2b/0x30
[ 1583.112086]  [<c02a281c>] dma_debug_device_change+0x13c/0x180
[ 1583.112142]  [<c03e6c33>] notifier_call_chain+0x53/0x90
[ 1583.112198]  [<c03e1ebe>] ? down_read+0x6e/0x90
[ 1583.112271]  [<c015b229>] __blocking_notifier_call_chain+0x49/0x70
[ 1583.112326]  [<c015b26f>] blocking_notifier_call_chain+0x1f/0x30
[ 1583.112380]  [<c031931c>] __device_release_driver+0x8c/0xa0
[ 1583.112451]  [<c03193bf>] driver_detach+0x8f/0xa0
[ 1583.112538]  [<c0318382>] bus_remove_driver+0x82/0x100
[ 1583.112595]  [<c0319ad9>] driver_unregister+0x49/0x80
[ 1583.112671]  [<c024feb2>] ? sysfs_remove_file+0x12/0x20
[ 1583.112727]  [<c02aa292>] pci_unregister_driver+0x32/0x80
[ 1583.112791]  [<fc13a3c1>] iwl_exit+0x12/0x19 [iwlagn]
[ 1583.112848]  [<c017940a>] sys_delete_module+0x15a/0x210
[ 1583.112870]  [<c015a5db>] ? up_read+0x1b/0x30
[ 1583.112893]  [<c029600c>] ? trace_hardirqs_off_thunk+0xc/0x10
[ 1583.112924]  [<c0295ffc>] ? trace_hardirqs_on_thunk+0xc/0x10
[ 1583.112947]  [<c03e6a1f>] ? do_page_fault+0x1ff/0x3c0
[ 1583.112978]  [<c03e36f6>] ? restore_all_notrace+0x0/0x18
[ 1583.113002]  [<c016aa70>] ? trace_hardirqs_on_caller+0x20/0x190
[ 1583.113025]  [<c0102d58>] sysenter_do_call+0x12/0x38
[ 1583.113054] ---[ end trace fc23e059cc4c2ced ]---

Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>