ath6kl: Fix random system lockup

ath6kl: Fix random system lockup

The commit "ath6kl: Use a mutex_lock to avoid
race in diabling and handling irq" introduces a
state where ath6kl_sdio_irq_handler() would be waiting
to claim the sdio function for receive indefinitely
when things happen in the following order.

ath6kl_sdio_irq_handler()
	- aquires mtx_irq
	- sdio_release_host()
					ath6kl_sdio_irq_disable()
						- sdio_claim_host()
						- sleep on mtx_irq
	ath6kl_hif_intr_bh_handler()
		- (indefinitely) wait for the sdio
		  function to be released to exclusively claim
		  it again for receive operation.

Fix this by replacing the mtx_irq with an atomic
variable and a wait_queue.

kvalo: add ath6kl_sdio_is_on_irq() due to open parenthesis alignment

Signed-off-by: Raja Mani <rmani@qca.qualcomm.com>
Signed-off-by: Vasanthakumar Thiagarajan <vthiagar@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>