rt2x00usb: fix anchor initialization

If device fail to initialize we can OOPS in rt2x00lib_remove_dev(), due
to using uninitialized usb_anchor structure:

[  855.435820] ieee80211 phy3: rt2x00usb_vendor_request: Error - Vendor Request 0x07 failed for offset 0x1000 with error -19
[  855.435826] ieee80211 phy3: rt2800_probe_rt: Error - Invalid RT chipset 0x0000, rev 0000 detected
[  855.435829] ieee80211 phy3: rt2x00lib_probe_dev: Error - Failed to allocate device
[  855.435845] BUG: unable to handle kernel NULL pointer dereference at 0000000000000028
[  855.435900] IP: _raw_spin_lock_irq+0xd/0x30
[  855.435926] PGD 0
[  855.435953] Oops: 0002 [#1] SMP
<snip>
[  855.437011] Call Trace:
[  855.437029]  ? usb_kill_anchored_urbs+0x27/0xc0
[  855.437061]  rt2x00lib_remove_dev+0x190/0x1c0 [rt2x00lib]
[  855.437097]  rt2x00lib_probe_dev+0x246/0x7a0 [rt2x00lib]
[  855.437149]  ? ieee80211_roc_setup+0x9e/0xd0 [mac80211]
[  855.437183]  ? __kmalloc+0x1af/0x1f0
[  855.437207]  ? rt2x00usb_probe+0x13d/0xc50 [rt2x00usb]
[  855.437240]  rt2x00usb_probe+0x155/0xc50 [rt2x00usb]
[  855.437273]  rt2800usb_probe+0x15/0x20 [rt2800usb]
[  855.437304]  usb_probe_interface+0x159/0x2d0
[  855.437333]  driver_probe_device+0x2bb/0x460

Patch changes initialization sequence to fix the problem.

Cc: Vishal Thanki <vishalthanki@gmail.com>
Fixes: 8b4c0009 ("rt2x00usb: Use usb anchor to manage URB")
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>