ath10k: fix error while writing 'simulate_fw_crash' debugfs

Fix invalid argument error while writing 'simulate_fw_crash',
though the funcionality is working fine we get an error 'invalid
argument' because 'count' value is not returned properly
(no reason to reduce the count value for removing the newline)

Fixes the below write error:

/sys/kernel/debug/ieee80211/phy0/ath10k# echo hw-restart >
simulate_fw_crash
-bash: echo: write error: Invalid argument

Also move the 'conf_mutex' as it is really not required for
fetching the userspace buffer.

Reported-by: Maharaja Kennadyrajan <c_mkenna@qti.qualcomm.com>
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qti.qualcomm.com>
Signed-off-by: Maharaja Kennadyrajan <c_mkenna@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>