usb: gadget: composite: Clear "suspended" on reset/disconnect

In some cases, one can get out of suspend with a reset or
a disconnect followed by a reconnect. Previously we would
leave a stale suspended flag set.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>