usb: gadget: f_mass_storage: stop thread in bind failure case

After the worker thread is launched, bind function is doing further
configuration. In case of failure stop the thread.

Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Sanjay Singh Rawat <snjsrwt@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>