rpmsg: glink: Fix rpmsg_register_device err handling

The device release function is set before registering with rpmsg. If
rpmsg registration fails, the framework will call device_put(), which
invokes the release function. The channel create logic does not need to
free rpdev if rpmsg_register_device() fails and release is called.

Change-Id: I66d3cc02eb5503130c6ad700a7e000054e8992f3
Signed-off-by: Chris Lew <clew@codeaurora.org>