musb->int_usb already contains the correct
information for musb-core to handle babble.

In fact, this very check was just causing a
nonsensical babble interrupt storm.

With this I can get test.sh to run and, even though
all tests fail with timeout, that's still better
than locking up the system due to IRQ storm.

Also, if I remove g_zero and load g_mass_storage,
then everything works fine again.

Tested-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>