USB: legousbtower: fix open after failed reset request

The driver would return with a nonzero open count in case the reset
control request failed. This would prevent any further attempts to open
the char dev until the device was disconnected.

Fix this by incrementing the open count only on successful open.

Fixes: 1da177e4

 ("Linux-2.6.12-rc2")
Signed-off-by: Johan Hovold <johan@kernel.org>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20190919083039.30898-5-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>