brcmfmac: Fix warning message after dongle setup failed

Brcmfmac showed warning message in fweh.c when checking the size of event
queue which is not initialized. Therefore, we only cancel the worker and
reset event handler only when it is initialized.

[  145.505899] brcmfmac 0000:02:00.0: brcmf_pcie_setup: Dongle setup
[  145.929970] ------------[ cut here ]------------
[  145.929994] WARNING: CPU: 0 PID: 288 at drivers/net/wireless/broadcom/brcm80211/brcmfmac/fweh.c:312
brcmf_fweh_detach+0xbc/0xd0 [brcmfmac]
...
[  145.930029] Call Trace:
[  145.930036]  brcmf_detach+0x77/0x100 [brcmfmac]
[  145.930043]  brcmf_pcie_remove+0x79/0x130 [brcmfmac]
[  145.930046]  pci_device_remove+0x39/0xc0
[  145.930048]  device_release_driver_internal+0x141/0x200
[  145.930049]  device_release_driver+0x12/0x20
[  145.930054]  brcmf_pcie_setup+0x101/0x3c0 [brcmfmac]
[  145.930060]  brcmf_fw_request_done+0x11d/0x1f0 [brcmfmac]
[  145.930062]  ? lock_timer_base+0x7d/0xa0
[  145.930063]  ? internal_add_timer+0x1f/0xa0
[  145.930064]  ? add_timer+0x11a/0x1d0
[  145.930066]  ? __kmalloc_track_caller+0x18c/0x230
[  145.930068]  ? kstrdup_const+0x23/0x30
[  145.930069]  ? add_dr+0x46/0x80
[  145.930070]  ? devres_add+0x3f/0x50
[  145.930072]  ? usermodehelper_read_unlock+0x15/0x20
[  145.930073]  ? _request_firmware+0x288/0xa20
[  145.930075]  request_firmware_work_func+0x36/0x60
[  145.930077]  process_one_work+0x144/0x360
[  145.930078]  worker_thread+0x4d/0x3c0
[  145.930079]  kthread+0x112/0x150
[  145.930080]  ? rescuer_thread+0x340/0x340
[  145.930081]  ? kthread_park+0x60/0x60
[  145.930083]  ret_from_fork+0x25/0x30

Signed-off-by: Wright Feng <wright.feng@cypress.com>
Signed-off-by: Chi-hsien Lin <chi-hsien.lin@cypress.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200928054922.44580-3-wright.feng@cypress.com