ath6kl: Fix kernel panic while receiving fwlog during boot

"ath6kl: Defer wiphy and netdev registration till the end of ath6kl_core_init()"
causes kernel panic by accessing the unallocated debug resources during
boot time. To fix this, split the debug initialization funtion into two,
one initializes the debug resource and the other takes care of debugfs
initialization. When this issue shows up the kernel crash dump would
look like

 ath6kl_debug_fwlog_event+0x9c/0x10a
 [<c10666c9>] register_lock_class+0x57/0x288
 [<c1065cd3>] ? trace_hardirqs_on+0xb/0xd
 [<f801f4c9>] ? ath6kl_debug_fwlog_event+0x9c/0x10a
 [<c1066a8a>] __lock_acquire+0x96/0xbe5
 [<c106007b>] ? alarmtimer_suspend+0x80/0x127
 [<c10258da>] ? vprintk+0x394/0x3b1
 [<f801f4c9>] ? ath6kl_debug_fwlog_event+0x9c/0x10a
 [<c10676b3>] lock_acquire+0xda/0xf9
 [<f801f4c9>] ? ath6kl_debug_fwlog_event+0x9c/0x10a
 [<c1532ce3>] _raw_spin_lock+0x28/0x58
 [<f801f4c9>] ? ath6kl_debug_fwlog_event+0x9c/0x10a
 [<f801f4c9>] ath6kl_debug_fwlog_event+0x9c/0x10a
 [<f80310a4>] ath6kl_wmi_control_rx+0x69d/0xb50 [ath6kl_core]
 [<f802d2e1>] ? ath6kl_rx+0x3c/0x839 [ath6kl_core]
 [<f802d35d>] ath6kl_rx+0xb8/0x839 [ath6kl_core]
 [<c104b81e>] ? local_clock+0x2d/0x4e
 [<c102a0af>] ? _local_bh_enable_ip+0x94/0x98
 [<f802bfc0>] ? ath6kl_alloc_amsdu_rxbuf+0xb7/0xb7
 [<f8023b28>] ath6kl_htc_rxmsg_pending_handler+0x891/0x988 [ath6kl_core]
 [<f802bf00>] ? ath6kl_refill_amsdu_rxbufs+0x89/0x92
 [<f802d2a5>] ? aggr_timeout+0xed/0xed [ath6kl_core]
 [<f802bfc0>] ? ath6kl_alloc_amsdu_rxbuf+0xb7/0xb7
 [<f802c420>] ? ath6kl_tx_complete+0x376/0x376 [ath6kl_core]
 [<f8020e92>] ath6kl_hif_intr_bh_handler+0xf7/0x33e
 [<c138ab00>] ? mmc_host_disable+0x15/0x3a
 [<f8123b5c>] ath6kl_sdio_irq_handler+0x3c/0x90 [ath6kl_sdio]
 [<c1392f56>] sdio_irq_thread+0xb6/0x29c
 [<c1392ea0>] ? sdio_claim_irq+0x1cb/0x1cb
 [<c103d4c0>] kthread+0x67/0x6c
 [<c103d459>] ? __init_kthread_worker+0x42/0x42
 [<c153903a>] kernel_thread_helper+0x6/0xd
 BUG: unable to handle kernel NULL pointer dereference at
EIP: [<f801f4d4>] ath6kl_debug_fwlog_event+0xa7/0x10a

kvalo: rename new function to ath6kl_debug_init_fs() and add a comment
why it's needed

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