If MediaTek's Bluetooth setup is unsuccessful, a NULL pointer issue
occur when the system is suspended and the anchored kill function
is called. To avoid this, add protection to prevent executing the
anchored kill function if the setup is unsuccessful.

[    6.922106] Hardware name: Acer Tomato (rev2) board (DT)
[    6.922114] Workqueue: pm pm_runtime_work
[    6.922132] pstate: 804000c9
(Nzcv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[    6.922147] pc : usb_kill_anchored_urbs+0x6c/0x1e0
[    6.922164] lr : usb_kill_anchored_urbs+0x48/0x1e0
[    6.922181] sp : ffff800080903b60
[    6.922187] x29: ffff800080903b60
x28: ffff2c7b85c32b80 x27: ffff2c7bbb370930
[    6.922211] x26: 00000000000f4240
x25: 00000000ffffffff x24: ffffd49ece2dcb48
[    6.922255] x20: ffffffffffffffd8
x19: 0000000000000000 x18: 0000000000000006
[    6.922276] x17: 6531656337386238
x16: 3632373862333863 x15: ffff800080903480
[    6.922297] x14: 0000000000000000
x13: 303278302f303178 x12: ffffd49ecf090e30
[    6.922318] x11: 0000000000000001
x10: 0000000000000001 x9 : ffffd49ecd2c5bb4
[    6.922339] x8 : c0000000ffffdfff
x7 : ffffd49ecefe0db8 x6 : 00000000000affa8
[    6.922360] x5 : ffff2c7bbb35dd48
x4 : 0000000000000000 x3 : 0000000000000000
[    6.922379] x2 : 0000000000000000
x1 : 0000000000000003 x0 : ffffffffffffffd8
[    6.922400] Call trace:
[    6.922405]  usb_kill_anchored_urbs+0x6c/0x1e0
[    6.922422]  btmtk_usb_suspend+0x20/0x38
[btmtk 5f200a97badbdfda4266773fee49acfc8e0224d5]
[    6.922444]  btusb_suspend+0xd0/0x210
[btusb 0bfbf19a87ff406c83b87268b87ce1e80e9a829b]
[    6.922469]  usb_suspend_both+0x90/0x288
[    6.922487]  usb_runtime_suspend+0x3c/0xa8
[    6.922507]  __rpm_callback+0x50/0x1f0
[    6.922523]  rpm_callback+0x70/0x88
[    6.922538]  rpm_suspend+0xe4/0x5a0
[    6.922553]  pm_runtime_work+0xd4/0xe0
[    6.922569]  process_one_work+0x18c/0x440
[    6.922588]  worker_thread+0x314/0x428
[    6.922606]  kthread+0x128/0x138
[    6.922621]  ret_from_fork+0x10/0x20
[    6.922644] Code: f100a274 54000520 d503201f d100a260 (b8370000)
[    6.922654] ---[ end trace 0000000000000000 ]---

Fixes: ceac1cb0 ("Bluetooth: btusb: mediatek: add ISO data transmission functions")
Signed-off-by: Chris Lu <chris.lu@mediatek.com>
Reported-by: Nícolas F. R. A. Prado <nfraprado@collabora.com> #KernelCI
Tested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>