iwlwifi: Fix double-free problems in iwl_req_fw_callback()

In the error handling code of iwl_req_fw_callback(), iwl_dealloc_ucode()
is called to free data. In iwl_drv_stop(), iwl_dealloc_ucode() is called
again, which can cause double-free problems.

To fix this bug, the call to iwl_dealloc_ucode() in
iwl_req_fw_callback() is deleted.

This bug is found by a runtime fuzzing tool named FIZZER written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>