bdc: Fix bug causing crash after multiple disconnects

[ Upstream commit a95bdfd22076497288868c028619bc5995f5cc7f ]

Multiple connects/disconnects can cause a crash on the second
disconnect. The driver had a problem where it would try to send
endpoint commands after it was disconnected which is not allowed
by the hardware. The fix is to only allow the endpoint commands
when the endpoint is connected. This will also fix issues that
showed up when using configfs to create gadgets.

Signed-off-by: Sasi Kumar <sasi.kumar@broadcom.com>
Signed-off-by: Al Cooper <alcooperx@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>