btusb: Avoid reset of ISOC endpoint alt settings to zero

In case of suspend/resume and HCI_RESET (BT On and Off),
ISOC endpoint set to alt setting 0 when no SCO connection exists.
This patch shall avoid resetting of ISOC endpoint to alt setting to 0.

Signed-off-by: Chethan Tumkur Narayan <chethan.tumkur.narayan@intel.com>
Signed-off-by: Kiran K <kiran.k@intel.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>