Bluetooth: btmtk: fix error handling in btmtk_usb_isointf_init()

btmtk_usb_isointf_init() submits the ISO interrupt IN URB and then
sends the vendor command 0xfd98. If that command fails, the function
returns an error without killing the URB it has just submitted. The
caller then leaves BTMTK_ISOPKT_RUNNING clear, so the driver treats the
ISO path as inactive while its RX URB is still in flight, and
btmtk_usb_suspend() skips killing it. Kill the anchored URBs on this
path, as the URB submission failure path already does.

The return value of __set_mtk_intr_interface() is also ignored: a
failure to select the ISO alternate setting or to find its endpoints
is logged, but the function goes on to submit the URB. Return the
error instead.

Fixes: ceac1cb0259d ("Bluetooth: btusb: mediatek: add ISO data transmission functions")
Signed-off-by: Ismail Tarim <ismailtarim7@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>