Bluetooth: hci_qca: Remove set but not used variable 'opcode'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/bluetooth/hci_qca.c: In function 'qca_controller_memdump':
drivers/bluetooth/hci_qca.c:980:6: warning:
 variable 'opcode' set but not used [-Wunused-but-set-variable]

It is never used since commit d841502c ("Bluetooth: hci_qca: Collect
controller memory dump during SSR"), so remove it.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>