ath9k: Fix a dma warning/memory leak

proper dma_unmapping and freeing of skb's has to be done in the rx
cleanup for EDMA chipsets when the device is unloaded and this also
seems to address the following warning which shows up occasionally when
the device is unloaded

	Call Trace:
	[<c0148cd2>] warn_slowpath_common+0x72/0xa0
	[<c03b669c>] ? dma_debug_device_change+0x19c/0x200
	[<c03b669c>] ? dma_debug_device_change+0x19c/0x200
	[<c0148da3>] warn_slowpath_fmt+0x33/0x40
	[<c03b669c>] dma_debug_device_change+0x19c/0x200
	[<c0657f12>] notifier_call_chain+0x82/0xb0
	[<c0171370>] __blocking_notifier_call_chain+0x60/0x90
	[<c01713bf>] blocking_notifier_call_chain+0x1f/0x30
	[<c044f594>] __device_release_driver+0xa4/0xc0
	[<c044f647>] driver_detach+0x97/0xa0
	[<c044e65c>] bus_remove_driver+0x6c/0xe0
	[<c029af0b>] ? sysfs_addrm_finish+0x4b/0x60
	[<c0450109>] driver_unregister+0x49/0x80
	[<c0299f54>] ? sysfs_remove_file+0x14/0x20
	[<c03c3ab2>] pci_unregister_driver+0x32/0x80
	[<f92c2162>] ath_pci_exit+0x12/0x20 [ath9k]
	[<f92c8467>] ath9k_exit+0x17/0x36 [ath9k]
	[<c06523cd>] ? mutex_unlock+0xd/0x10
	[<c018e27f>] sys_delete_module+0x13f/0x200
	[<c02139bb>] ? sys_munmap+0x4b/0x60
	[<c06547c5>] ? restore_all+0xf/0xf
	[<c0657a20>] ? spurious_fault+0xe0/0xe0
	[<c01832f4>] ? trace_hardirqs_on_caller+0xf4/0x180
	[<c065b863>] sysenter_do_call+0x12/0x38
	 ---[ end trace 16e1c1521c06bcf9 ]---
	Mapped at:
	[<c03b7938>] debug_dma_map_page+0x48/0x120
	[<f92ba3e8>] ath_rx_init+0x3f8/0x4b0 [ath9k]
	[<f92b5ae4>] ath9k_init_device+0x4c4/0x7b0 [ath9k]
	[<f92c2813>] ath_pci_probe+0x263/0x330 [ath9k]

Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>