rsi: fix occasional initialisation failure with BT coex

When BT coexistence is enabled (eg oper mode 13, which is the default)
the initialisation on startup sometimes silently fails.

In a normal initialisation we see
	usb 1-1.3: Product: Wireless USB Network Module
	usb 1-1.3: Manufacturer: Redpine Signals, Inc.
	usb 1-1.3: SerialNumber: 000000000001
	rsi_91x: rsi_probe: Initialized os intf ops
	rsi_91x: rsi_load_9116_firmware: Loading chunk 0
	rsi_91x: rsi_load_9116_firmware: Loading chunk 1
	rsi_91x: rsi_load_9116_firmware: Loading chunk 2
	rsi_91x: Max Stations Allowed = 1

But sometimes the last log is missing and the wlan net device is
not created.

Running a userspace loop that resets the hardware via a GPIO shows the
problem occurring ~5/100 resets.

The problem does not occur in oper mode 1 (wifi only).

Adding logs shows that the initialisation state machine requests a MAC
reset via rsi_send_reset_mac() but the firmware does not reply, leading
to the initialisation sequence being incomplete.

Fix this by delaying attaching the BT adapter until the wifi
initialisation has completed.

With this applied I have done > 300 reset loops with no errors.

Fixes: 716b840c7641 ("rsi: handle BT traffic in driver")
Signed-off-by: Martin Fuzzey <martin.fuzzey@flowbird.group>
CC: stable@vger.kernel.org
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1630337206-12410-2-git-send-email-martin.fuzzey@flowbird.group

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